Creating Italian Sausage & Pepper Casserole is simple if you follow these easy steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Cook the Sausage: In a large skillet over medium heat, add the Italian sausage. Break it up with a spatula and cook until browned, about 5-7 minutes. Drain excess fat if necessary.
3. Add Vegetables: Add the sliced onion, bell peppers, and minced garlic to the skillet. Sauté for about 5 minutes, or until the vegetables are tender.
4. Combine Ingredients: Stir in the diced tomatoes, oregano, basil, red pepper flakes (if using), salt, and pepper. Let it simmer for another 5 minutes.
5. Mix with Pasta: In a large bowl, combine the cooked pasta with the sausage and vegetable mixture. Mix well to ensure everything is evenly distributed.
6. Prepare for Baking: Transfer the mixture into a greased 9×13 inch baking dish. Spread it evenly.
7. Add Cheese: Sprinkle the shredded mozzarella and grated Parmesan cheese evenly over the top of the casserole.
8. Bake: Place the casserole in the preheated oven and bake for 25-30 minutes or until the cheese is bubbly and golden brown.
9. Cool Down: Remove from the oven and let it cool for about 10-15 minutes before serving.
10. Garnish and Serve: If desired, garnish with fresh basil before serving.

These steps will guide you in creating this incredible Italian Sausage & Pepper Casserole effortlessly.