All you need it a one-step angel food cake mix and a 15 oz. can of lemon pie filling.
powdered sugar for dusting
Mix the cake mix & the pie filling together by hand until moist. Be sure not to over stir. Bake in a 9x13 cake pan at 350 degrees until golden brown on the top (about 20 minutes). Cool completely before eating. As they are cooling, you can sprinkle with powder sugar if you wish (Which I guess technically makes this a 3-ingredient recipe). They have more of an angel food cake texture than a traditional lemon bar texture.