Preheat the oven to 375°F (190°C).
Cook the penne pasta according to package instructions; drain and set aside.
In a large mixing bowl, combine the cooked chicken, Alfredo sauce, garlic powder, salt, and pepper.
Stir in half of the mozzarella cheese and all of the cooked pasta.
Transfer the mixture into a greased 9x13 inch baking dish.
Sprinkle the remaining mozzarella and Parmesan cheese evenly over the top.
Bake uncovered for 25–30 minutes, or until bubbly and golden.
Garnish with chopped parsley before serving, if desired.