Preheat your oven to 350°F (175°C).
Cook the penne pasta according to package directions until al dente, then drain and set aside.
In a large mixing bowl, combine the cooked chicken, broccoli florets, cooked pasta, Alfredo sauce, garlic powder, salt, and pepper.
Transfer the mixture into a greased 9x13 inch casserole dish.
Sprinkle the shredded mozzarella and grated Parmesan cheese evenly over the top.
Bake in the preheated oven for 30-35 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it cool for a few minutes before serving.
