1 (9-10 inch) angel food cake
1 (21 oz.) can or 1 box lemon filling or topping
1 (8 oz.) carton lemon yogurt
1 (8 oz.) Cool Whip, thawed

Cut cake into four layers. In medium bowl, combine pie filling (prepared) and yogurt. Blend well. Spread 1/3 of mixture between each layer. Frost top and sides with whipped topping. Garnish with lemon slices. Refrigerate.