Open the can of Lemon Pie Filling, and add the Pie Filling to the Cake Mix. Stir together until well mixed, and no cake mix is visible. The Batter will be fluffy, and foam up a little.
Pour into a 9x13 dish (un-greased) and bake at 350 degrees for 25 to 30 minutes. The Cake will rise above the dish in the oven, but will settle when removed.
When the Cake is done, remove from the oven to a wire rack, and allow to cool completely.
Cut into 3x3 inch squares.
Sprinkle with Powdered Sugar and top with whipped cream if desired.