Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add one finely chopped onion and sauté for 3-4 minutes until it becomes translucent. Toss in 4 minced garlic cloves, 2 diced medium carrots, and 1 red and 1 yellow diced bell pepper. Cook for an additional 5-7 minutes, stirring occasionally.

Push the sautéed vegetables to the side of the skillet and add 1.5 pounds of ground beef into the vacant space. Allow it to brown for about 5-7 minutes, breaking it up with a wooden spoon until no pink remains. Drain any excess fat.

Stir in 2 cups of tomato sauce, 1 can of drained diced tomatoes, and 1 cup of beef broth to the beef and vegetable mixture. Sprinkle in 2 teaspoons of Italian seasoning, along with salt and pepper to taste. Bring to a gentle simmer over medium heat, cooking for 10 minutes.

Preheat the oven to 375°F (190°C). Pour the filling into a casserole dish. Sprinkle 1 cup of shredded cheese over the top, and optionally add ½ cup of breadcrumbs.

Bake for 25-30 minutes, until the cheese is bubbly and golden brown. Once baked, let it cool for 5-10 minutes before serving.