Preheat your oven to 375 degrees Fahrenheit (190 degrees Celsius). Lightly grease a 9×13 inch baking dish.
Cook the pasta according to package directions until al dente. Drain well.
In a large bowl, combine the drained pasta, cooked chicken, Alfredo sauce, heavy cream, Parmesan cheese, garlic powder, pepper, and salt. Mix until everything is evenly coated.
Pour the pasta mixture into the prepared baking dish, spreading it into an even layer.
Sprinkle the 2 cups of mozzarella cheese evenly over the top of the pasta mixture. If desired, drizzle the melted butter lightly over the cheese for extra browning.
Bake for 20 to 25 minutes, or until the sauce is bubbly around the edges and the mozzarella cheese is melted and lightly golden brown.
Remove from the oven and let it rest for 5 minutes before serving.
Notes
For the best texture, use low-moisture mozzarella cheese. Fresh mozzarella holds too much water.
You can cook the chicken by poaching or baking it before shredding.
If you prefer a richer sauce, substitute half of the heavy cream with cream cheese, softened.