Bottom Lemon Cake: In mixing bowl, combine cake mix, pie filling, and coconut. Stir until thoroughly mixed (do not add any liquid). Spread this mixture in a 10 by 15-inch baking pan. Bake for 30 minutes in a preheated 350 degree F oven. Cool.
Top Creamy Frosting: Combine all ingredients until blended well. Frost the Bottom Lemon Cake. Garnish with sprinkles of lemon zest and cut into 1 1/2 by 2 1/2-inch bars. Cover and refrigerate overnight for better flavoring.