Preheat the Oven to 425°F (220°C) and position the rack in the middle.

In a large pot, combine about 2 cups of water and steam both the cauliflower and broccoli florets covered for approximately 5 minutes until they become tender but not mushy.

In a large mixing bowl, combine the diced cooked chicken, softened cream cheese, half-and-half, and shredded mozzarella cheese. Season with garlic powder, onion powder, salt, and pepper. Mix thoroughly until all ingredients are well incorporated.

Stir in the warm, steamed broccoli and cauliflower into the cream cheese mixture while everything is still warm.

Carefully transfer the mixture into an oiled casserole dish, spreading it out evenly. Sprinkle a generous layer of the remaining mozzarella cheese on top.

Bake the casserole uncovered in your preheated oven for 10-15 minutes, or until the cheese is bubbly and starting to brown.

Switch your oven to broil for the last 3 minutes to enhance the golden crust, watching closely to avoid burning.