Preheat oven to 375°F. Lightly coat a 9-by-13-inch baking dish with cooking spray.
Stir broccoli, rice, Alfredo sauce, half-and-half and flour together in the prepared dish until well combined.
Top the mixture evenly with chicken; sprinkle with onion-and-herb seasoning, garlic powder, pepper and salt.
Sprinkle evenly with cheese. Cover tightly with foil.
Bake until a thermometer inserted into the chicken registers 165℉ and the cheese is melted, about 45 minutes.
Let stand for 10 minutes before serving.
