This 30-minute ground beef casserole is packed with protein, cheese, and veggies. An easy high-protein dinner perfect for busy weeknights. Save this quick casserole recipe!

Ingredients

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Instructions

Step 1

Preheat your oven to 375°F (190°C). While the oven heats, gather all your ingredients and prep the vegetables. Dicing the onion, zucchini, and bell pepper into uniform small cubes ensures even cooking. Mince the garlic finely to distribute its flavor throughout the dish. Drain the can of diced tomatoes to remove excess liquid, which helps prevent a watery casserole. Having everything prepped and ready (mise en place) makes the cooking process smooth and quick, especially for a 30-minute recipe.

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Step 2

Heat 1 tablespoon of olive oil in a large oven-safe skillet or Dutch oven over medium-high heat. Once the oil shimmers (about 30 seconds), add the diced onion. Sauté for 2-3 minutes until the onion becomes translucent and fragrant. Add the minced garlic and cook for another 30 seconds until aromatic, being careful not to burn the garlic. The oil should be hot enough to sizzle the onions but not smoking. This step builds the flavor base for the entire casserole.

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Step 3

Add the lean ground beef to the skillet. Break it apart with a wooden spoon or spatula into small crumbles. Cook for 5-6 minutes, stirring occasionally, until the beef is browned and no longer pink. If using 85/15 beef, you may need to drain excess fat after browning (leave about 1 tablespoon for flavor). For 90/10 beef, draining is usually unnecessary. The beef should be deeply browned with some crispy edges for maximum flavor. Do not overcrowd the pan; if necessary, cook in batches to ensure proper browning.

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Step 4

Add the diced zucchini and red bell pepper to the skillet with the beef. Stir to combine and cook for 3-4 minutes until the vegetables begin to soften but still retain some crunch. The zucchini will release some moisture, which helps create a light sauce. Add the drained diced tomatoes, dried oregano, dried basil, salt, and pepper. Stir everything together and let it simmer for 2 minutes to meld the flavors. The mixture should be thick and aromatic, not soupy.

Step 5

Remove the skillet from heat. Sprinkle the shredded mozzarella cheese evenly over the top of the beef and vegetable mixture. Then sprinkle the grated Parmesan cheese over the mozzarella. The Parmesan adds a salty, nutty flavor and helps create a golden crust. Transfer the skillet to the preheated oven. Bake for 10-12 minutes until the cheese is melted, bubbly, and lightly browned around the edges. If you prefer a deeper golden crust, switch to broil for the last 1-2 minutes, watching carefully to avoid burning.

Step 6

Remove the casserole from the oven and let it rest for 2-3 minutes. This allows the cheese to set slightly, making it easier to serve. Garnish with fresh basil if desired. Scoop onto plates or into bowls, ensuring each serving gets a generous portion of beef, veggies, and melted cheese. Serve hot. This casserole pairs well with a side salad or steamed green beans for extra vegetables. Leftovers can be stored in an airtight container in the refrigerator for up to 4 days.

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For best results

  • For the best flavor, use freshly grated Parmesan cheese instead of pre-shredded. Pre-shredded cheeses often contain anti-caking agents that prevent smooth melting, resulting in a grainy texture. Grating your own Parmesan from a block ensures a creamy, nutty melt that elevates the entire dish. You can also use a microplane for a fine, fluffy texture that distributes evenly.
  • To make this casserole even lower in carbs, replace the diced tomatoes with a can of tomato sauce (no added sugar) or use fresh Roma tomatoes that have been seeded and chopped. This reduces the sugar content while still providing the necessary acidity and moisture. Alternatively, you can skip the tomatoes altogether and add a splash of beef broth for moisture.
  • If you prefer a spicier kick, add 1/2 teaspoon of red pepper flakes or a diced jalapeño along with the garlic. For a smoky flavor, substitute 1/2 teaspoon of smoked paprika for the dried oregano. You can also use a Mexican cheese blend instead of mozzarella for a different flavor profile. Feel free to experiment with herbs like thyme or rosemary.
  • For meal prep, prepare the casserole up to the point of baking, then cover and refrigerate for up to 2 days. When ready to eat, bake as directed, adding 5-10 minutes to the cooking time since the dish starts cold. You can also freeze the unbaked casserole for up to 3 months. Thaw overnight in the refrigerator before baking. This makes for an incredibly convenient high-protein dinner on busy nights.
  • To ensure the ground beef browns properly, avoid stirring it too frequently. Let it sit undisturbed for 1-2 minutes after adding to the pan to develop a deep brown crust. This is called the Maillard reaction, which creates complex savory flavors. Once the bottom is browned, then break it apart and stir. This technique yields much more flavorful beef than constant stirring.
  • If you don't have an oven-safe skillet, you can transfer the beef mixture to a greased 9×13-inch baking dish before adding the cheese and baking. Alternatively, you can finish the casserole on the stovetop: after adding the cheese, cover the skillet and cook on low heat for 5-7 minutes until the cheese melts. However, oven baking gives a more even melt and attractive golden top.

Variations

  • Make it dairy-free by using dairy-free shredded mozzarella and Parmesan alternatives. Nutritional yeast can replace Parmesan for a cheesy flavor. The casserole will still be creamy and delicious. Also, ensure your diced tomatoes are free of added dairy ingredients. This variation works well for those with lactose intolerance or following a vegan diet (use plant-based ground meat substitute).
  • For a lower-fat version, use ground turkey or chicken instead of beef. Since poultry is leaner, add an extra tablespoon of olive oil to prevent dryness. You can also incorporate more vegetables like mushrooms, spinach, or kale. Mushrooms add umami, while spinach wilts down and boosts nutrients without altering flavor. This keeps the protein high while reducing saturated fat.
  • Transform this into a Tex-Mex casserole by adding 1 can of black beans (drained and rinsed), 1/2 cup of corn kernels, and 1 teaspoon of chili powder. Replace the oregano and basil with cumin and smoked paprika. Top with shredded cheddar or a Mexican blend, and serve with avocado slices, salsa, and a dollop of Greek yogurt. This version is higher in fiber and still packed with protein.
  • Make it a one-pot pasta casserole by adding 2 cups of cooked pasta (such as penne or rotini) to the beef mixture before topping with cheese. Stir in 1/2 cup of pasta water to help the sauce coat the noodles. Bake as directed. This turns the dish into a hearty, complete meal that's perfect for feeding a crowd. Adjust seasoning as needed, since pasta absorbs flavors.

Nutrition

  • Calories385 kcal
  • Total Fat22g
  • Saturated Fat9g
  • Cholesterol85mg
  • Sodium520mg
  • Total Carbohydrates12g
  • Dietary Fiber3g
  • Sugars6g
  • Protein35g

Common Questions

Can I use ground turkey instead of beef?
Absolutely! Ground turkey is a great lean alternative. Since turkey is leaner, add an extra tablespoon of olive oil to prevent dryness. Cook until it reaches an internal temperature of 165°F. The flavor will be slightly milder, so you may want to boost the herbs and spices. You can also use ground chicken or a plant-based ground meat substitute for a vegetarian option.
How do I store leftovers and how long do they last?
Store leftovers in an airtight container in the refrigerator for up to 4 days. Reheat in the microwave or oven at 350°F until warmed through. To freeze, let the casserole cool completely, then transfer to a freezer-safe container. It will keep for up to 3 months. Thaw overnight in the fridge before reheating. The texture may change slightly upon thawing, but it will still be delicious.
Can I make this casserole ahead of time?
Yes, you can assemble the casserole up to 2 days in advance. Prepare the beef and vegetable mixture, transfer to a baking dish, cover, and refrigerate. When ready to bake, add the cheese and bake as directed, adding 5-10 minutes to the cooking time since the dish starts cold. You can also freeze the unbaked casserole for up to 3 months. This makes it perfect for meal prep.
What can I use instead of mozzarella?
You can substitute mozzarella with provolone, Monterey Jack, cheddar, or a Italian cheese blend. Each cheese will impart a different flavor: provolone is mild and melts well, cheddar adds sharpness, and Monterey Jack is creamy. For a dairy-free option, use dairy-free shredded cheese. The cooking time remains the same regardless of cheese choice.
Is this casserole keto-friendly?
This casserole is low in carbs and can be considered keto-friendly if you use tomato sauce instead of diced tomatoes (to reduce sugar) or omit the tomatoes entirely. The net carbs per serving are approximately 8-10 grams, which fits within a standard keto diet. The high fat from cheese and beef also aligns with keto macros. For stricter keto, use full-fat cheese and ground beef with higher fat content.
How can I add more vegetables?
This casserole is very versatile. You can add mushrooms, spinach, kale, broccoli florets (chopped small), or cauliflower rice. Sauté any harder vegetables like broccoli with the onion, and add softer greens like spinach at the end just to wilt. Increase the seasoning slightly to account for the extra bulk. Adding more veggies boosts fiber and nutrients without significantly increasing calories.
Can I use fresh tomatoes instead of canned?
Yes, use 2 medium fresh Roma tomatoes, seeded and diced. Fresh tomatoes have less liquid than canned, so you may need to add 2-3 tablespoons of water or broth to prevent dryness. They also have a brighter, less concentrated flavor, so consider adding a tablespoon of tomato paste for depth. Cooking time remains the same.