In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the finely chopped onion, sautéing for 3-4 minutes until translucent. Stir in minced garlic, diced carrots, and diced bell peppers. Cook until tender.

Push the sautéed vegetables to one side and add 1.5 pounds of lean ground beef to the other side. Cook for 5-7 minutes until browned, then drain excess fat.

Combine the cooked beef with the vegetables. Add tomato sauce, drained diced tomatoes, and beef broth. Sprinkle with Italian seasoning and season with salt and pepper. Simmer for about 10 minutes.

Preheat oven to 375°F (190°C). Pour the mixture into a casserole dish. Optional: sprinkle breadcrumbs and top with cheese.

Bake for 25-30 minutes until cheese is bubbly and golden brown.

Allow the casserole to cool for 5-10 minutes before serving.