Preheat oven to 350. Prepare a 13" x 9" pan with cooking spray and flour; set aside. In a mixing bowl, combine cake mix, dry pudding mix, egg whites, water, oil, peppermint extract, green food coloring, and chocolate chips. Mix well. Pour into prepared pan. Bake for 35 minutes, or until light brown on top. Remove cake from oven. Place candies in a single layer on top of cake to cover. Return to oven for three minutes or until candies have melted. Remove from oven again and quickly spread melted candies evenly over cake.