Preheat the oven to 350°F.

Spray a 9x13-inch baking dish with nonstick cooking spray. Set aside.

Place the rice, chicken, corn, creamed corn, scallions, evaporated milk, sour cream, salt, black pepper, garlic powder, Parmesan cheese, and cheddar cheese in a large mixing bowl. Stir the ingredients with a wooden spoon until everything is well combined.

Transfer the mixture to the prepared casserole dish and smooth it into an even layer. Sprinkle desired amount of shredded cheese evenly over the top.

Bake the casserole on middle rack of oven until the cheese is golden brown and dish is gently bubbling at the edges, 40-45 minutes.

Check to see that casserole is done. Remove from oven or add time as needed.

Let the casserole cool for 10-15 minutes before serving.