Step 1: Sauté the Vegetables. Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook for about 3–4 minutes until it softens and turns translucent. Stir in the minced garlic and cook for another minute until fragrant — be careful not to let it burn. Add the diced carrots and bell peppers and sauté for 5–7 minutes, until tender but still slightly crisp. This builds a flavorful base for your casserole.

Step 2: Brown the Beef. Push the vegetables to the side of the skillet and add the ground beef to the center. Break it apart with a wooden spoon and cook for 5–7 minutes, stirring occasionally, until browned and no longer pink. Drain any excess fat to prevent the casserole from becoming greasy.

Step 3: Build the Sauce. Stir the cooked vegetables back into the beef. Add tomato sauce, diced tomatoes, and beef broth. Season with Italian seasoning, salt, and pepper. Stir well, then bring the mixture to a gentle simmer. Let it cook uncovered for about 10 minutes, allowing the flavors to meld and the sauce to thicken slightly.

Step 4: Assemble the Casserole. Preheat your oven to 375°F (190°C). Pour the beef and vegetable mixture into a greased 9x13-inch casserole dish. If using, sprinkle breadcrumbs evenly over the top for a crunchy layer. Then, generously top with shredded cheese, spreading it evenly to cover the entire surface.

Step 5: Bake to Perfection. Place the casserole in the preheated oven and bake for 25–30 minutes, or until the cheese is melted, bubbly, and beautifully golden.

Step 6: Cool and Serve. Once baked, remove from the oven and let it rest for 5–10 minutes before serving. This helps the casserole set slightly and makes it easier to serve neat portions. Garnish with freshly chopped basil or parsley for a burst of color and flavor.