Spray The Inside Of A 4-Quart Slow Cooker With The Cooking Spray. Place The Chicken Into The Cooker. Place 1 Tablespoon Of Butter Onto Each Chicken Breast Half. Stir The Onion Soup Mix, Mushroom Soup, Milk And Rice In A Medium Bowl. Pour Over The Chicken. Sprinkle With The Cheese. Cover And Cook On Low For 8 To 9 Hours* Or Until The Chicken Is Cooked Through.