01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or butter.
02 - Bring a large pot of salted water to boil. Cook pasta until al dente according to package directions. Drain well and set aside.
03 - Steam broccoli florets until just tender, about 3-4 minutes. Drain thoroughly to remove excess moisture.
04 - In a large mixing bowl, combine cooked pasta, diced chicken, steamed broccoli, Alfredo sauce, milk, garlic powder, Italian herbs, salt, and pepper. Add half of the mozzarella and Parmesan cheeses. Stir until evenly distributed.
05 - Transfer mixture to the prepared baking dish. Spread evenly with a spatula. Sprinkle remaining mozzarella and Parmesan cheese across the top in a uniform layer.
06 - Bake uncovered for 25-30 minutes, or until cheese is melted and bubbling with golden-brown spots on top.
07 - Remove from oven and let rest for 5 minutes before serving to allow the sauce to set slightly.