Italian Sausage and Pepper Casserole

1. Preheat oven to 375°F.
2. In a large skillet, cook Italian sausage until browned. Add in onion, bell peppers, and garlic, and cook until vegetables are softened.
3. Stir in diced tomatoes and season with salt and pepper.
4. Transfer sausage and pepper mixture to a casserole dish and top with shredded mozzarella cheese.
5. Bake in the oven for 20-25 minutes, or until cheese is melted and bubbly.