Preheat oven to 350 degrees D. Line a deep 9x13 inch baking pan with parchment paper.
In a large bowl, combine the box of angel food cake and lemon pie filling. Whisk it until it's well incorporated. Mix well until it starts to foam slightly.
Pour the batter in the baking pan and bake for 30 to 40 minutes. It's done when the edges have risen and have browned slightly and the center is set. I baked mine closer to 40 minutes, at 30 minutes it was not yet done.
Remove from the oven and cool on a wire rack. This cake cuts cleaner when completely cooled. Serve with ice cream or whipped cream and strawberries or blueberries, if desired.