Preheat oven to 375. Prepare a 8" square baking dish with cooking spray; set aside. In a mixing bowl, combine chicken, crushed crackers, onions, egg, chili powder, and salt. Mix well. Press into prepared dish. Bake for 25 minutes, or until juices run clear. Meanwhile, in another mixing bowl, combine potatoes and corn. Spread over loaf and sprinkle with cheese. Bake for ten more minutes, or until cheese has melted.