Heat olive oil in a large skillet over medium heat. Add the chopped onion and sauté for 3-4 minutes until translucent. Stir in minced garlic, diced carrots, and bell peppers, cooking everything together for an additional 5-7 minutes until softened.
Push the sautéed vegetables to one side of the skillet and add the ground beef to the other side. Cook until browned, breaking it apart with a spatula over about 5-7 minutes until fully cooked through.
Add tomato sauce, drained diced tomatoes, and beef broth to the skillet with the beef mixture. Stir in Italian seasoning along with salt and pepper according to your taste preferences, allowing it all to simmer together for approximately 10 minutes.
Preheat your oven to 375°F (190°C). Pour the beef mixture into a prepared casserole dish evenly spreading it out before topping it with shredded cheese and breadcrumbs if desired.
Place the casserole in the preheated oven and bake for 25-30 minutes or until the cheese is bubbly and golden brown on top. Let it cool for about 5-10 minutes before serving.