Preheat oven to 350. Prepare a 13" x 9" pan with cooking spray; set aside. In a mixing bowl, combine cake mix, dry pudding mix, eggs, water, oil, peppermint extract, green food coloring, and chocolate chips. Mix well. Pour into prepared pan. Bake for 25 minutes, or until lightly brown on top. Remove cake from oven. Place candies in a single layer on top of the cake to cover. Return to oven for five minutes or until candies have melted. Remove from oven again and quickly spread melted candies evenly over the cake.