Preheat your oven to 350°F (175°C).
Cook the penne pasta according to the package instructions until al dente. Drain, rinse, and set aside.
In a medium saucepan over medium heat, combine the butter, heavy cream, and cream cheese. Stir until smooth and fully melted.
Add the minced garlic, garlic powder, Italian seasoning, salt, and black pepper. Whisk until well combined.
Stir in the grated Parmesan cheese and simmer for 3–5 minutes until the sauce thickens slightly.
Place the cooked pasta into a large mixing bowl or back into the pasta pot. Pour the Alfredo sauce over the pasta and stir to coat evenly.
Fold in the cooked chicken until everything is well combined. This Baked Chicken Alfredo Pasta filling should be creamy and evenly coated.
Spread half of the pasta mixture into a greased 9×13-inch baking dish.
Sprinkle half of the mozzarella cheese over the pasta.
Add the remaining pasta mixture and finish with the remaining mozzarella and the extra Parmesan cheese.
Bake for 20–30 minutes until the cheese is melted, bubbly, and lightly golden.
Let the casserole rest for 5 minutes before serving.