Preheat your oven to 375°F (190°C).
In a large mixing bowl, combine the cooked pasta, broccoli, and chicken.
In a separate bowl, whisk together the heavy cream, Parmesan cheese, garlic powder, Italian seasoning, salt, and pepper until smooth.
Pour the cream mixture over the pasta, chicken, and broccoli, stirring until well coated.
Transfer the mixture to a greased 9x13-inch baking dish, spreading it evenly.
Sprinkle the shredded mozzarella cheese evenly on top of the casserole.
Cover the dish with foil and bake for 20 minutes.
Remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden.
Let the casserole rest for 5 minutes before serving.