Creating your Creamy Pasta Casserole is a breeze when you follow these simple steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Cook Pasta: Boil a large pot of salted water and cook the pasta according to package instructions until al dente. Drain and set aside.
3. Sauté Vegetables: In a large skillet, heat olive oil over medium heat. Add the diced onion and sauté until translucent. Add the minced garlic and cook for an additional minute.
4. Combine Ingredients: In the skillet, add the cooked chicken (if using), steamed broccoli, and chopped bell peppers. Stir to combine.
5. Make the Sauce: Pour in the heavy cream, and add Italian seasoning, salt, and pepper. Stir until well combined. Let it cook for about 3-5 minutes until slightly thickened.
6. Mix Pasta and Sauce: Add the drained pasta to the skillet and stir to coat the pasta with the creamy sauce.
7. Add Cheese: Stir in the mozzarella and cheddar cheeses until melted and fully incorporated.
8. Transfer to Casserole Dish: Pour the pasta mixture into a greased 9×13 inch casserole dish.
9. Top with Parmesan: Sprinkle the grated Parmesan cheese over the top of the casserole.
10. Bake: Place the casserole in the preheated oven and bake for 20-25 minutes or until bubbly and golden on top.
11. Cool Slightly: Once done, remove from the oven and let it sit for about 5 minutes before serving.

These steps will guide you through creating a delicious Creamy Pasta Casserole that will surely impress your family and friends.