Preheat oven to 350 degrees.
Add the broccoli to a large microwave safe bowl along with 2 tablespoons of water. Cover tightly with plastic wrap and microwave for 2 minutes. Let sit, covered, for 2 minutes.
Carefully remove the plastic wrap and drain the liquid.
Add the cream cheese, mayonnaise, cheddar, garlic powder, salt, and pepper to a small bowl and mix well to combine.
Stir the cream cheese mixture and chicken into the steamed broccoli until well combined.
Transfer broccoli to a 9x13 baking dish and sprinkle the Parmesan over the top.
Bake for 15 minutes.