Preheat your oven to 375°F (190°C).
Grease a baking dish and set it aside.
In a mixing bowl, combine the mayonnaise, sour cream, grated Parmesan cheese, chopped green onions, chopped parsley, garlic powder, onion powder, salt, and pepper. Mix well until all the ingredients are thoroughly combined.
In a separate large bowl, combine the cooked chicken and cooked white rice. Pour the mayo mixture over the chicken and rice. Stir until everything is evenly coated.
Transfer the mixture to the greased baking dish, spreading it out evenly.
Bake the chicken mayo rice bake in the preheated oven for 30-35 minutes, or until the top is golden brown and the casserole is heated through.
Remove from the oven and let it cool for a few minutes before serving. Garnish with additional chopped parsley, if desired.
Serve and enjoy the creamy and flavorful Chicken Mayo Rice Bake. It's perfect as a main course, accompanied by a side salad or steamed vegetables.