Preheat the oven to 375°F (190°C).
Steam the broccoli florets for 4-5 minutes until tender but still crisp. Drain well.
In a large mixing bowl, combine the shredded cooked chicken, steamed broccoli, condensed cream of chicken soup, sour cream, shredded cheddar cheese, grated Parmesan cheese, milk, garlic powder, onion powder, black pepper, and salt. Mix until well combined.
Transfer the chicken and broccoli mixture into a greased 9×13 inch casserole dish and spread evenly.
Open the refrigerated biscuit dough and separate the biscuits. Place the biscuits evenly spaced on top of the casserole mixture.
Brush the melted butter over the tops of the biscuits.
Bake in the preheated oven for 30-35 minutes, or until the biscuits are golden brown and cooked through and the casserole is bubbly.
Remove from the oven and let it cool for 5 minutes before serving.