Preheat Oven & Cook Pasta: Preheat your oven to 375°F (190°C). Cook the penne pasta according to package instructions until it is al dente (still firm to the bite). This typically takes about 8-10 minutes. Drain the pasta thoroughly and set it aside. Al dente pasta works best as it will continue cooking in the oven without becoming mushy.

Combine Ingredients: In a large mixing bowl, combine the cooked penne pasta, shredded chicken, Alfredo sauce, garlic powder, Italian seasoning, salt, and pepper. Mix gently but thoroughly until all ingredients are well combined and the pasta and chicken are evenly coated with the sauce. Be careful not to break the pasta while mixing.

Prepare Baking Dish: Lightly grease a 9×13 inch baking dish with olive oil. This prevents sticking and adds a subtle flavor to the edges of your casserole.

Assemble & Top: Pour the pasta mixture into the prepared baking dish, spreading it evenly with a spatula. Sprinkle the shredded mozzarella cheese and grated Parmesan cheese evenly over the top of the pasta mixture, creating a uniform layer that will melt into a golden crust.

Bake: Bake in the preheated oven for 25-30 minutes, or until the cheese is melted, golden brown, and bubbly, and the casserole is heated through. For a more golden top, you can broil for the last 1-2 minutes, but watch carefully to prevent burning.

Cool & Serve: Remove from the oven and let it cool for about 5 minutes before serving. This resting period allows the casserole to set slightly and makes it easier to portion. Garnish with fresh chopped parsley if desired for a pop of color and fresh flavor.