Preheat oven to 350 degrees and lightly spray a 9 x 13 baking pan with grease.
In a medium bowl, combine the chicken, broccoli, cream of chicken soup, rice, cheddar cheese, and mayonnaise.
Spread mixture evenly into prepared baking pan.
In small bowl, combine the cornflakes with melted butter. Set aside.
Sprinkle french onions evenly on top of chicken mixture.
Sprinkle cornflake mixture on top evenly.
Place pan into preheated oven and bake for 30 minutes. Serve!