1Heat oven to 350°F (325°F for dark or nonstick pans). Make, bake and cool cake as directed on box for two 8- or 9-inch rounds.
2In medium bowl, gently stir pie filling into frosting.
3Place 1 cake layer, rounded side down, on serving plate. Spread with 1 cup of the lemon mixture to within 1/4 inch of edge. Top with second layer. Frost side and top of cake with remaining lemon mixture. Store loosely covered.