Heat oven to 400°F (200°C) and grease and line 8-in. (20-cm) round cake pan according to package directions. Prepare cake batter according to package directions. Fold poppy seeds and lemon zest into batter. Scrape into prepared pan; smooth top.
Bake 29 to 33 min. and cool according to package directions. Using a large serrated knife, slice cake horizontally into two equal layers.
Place one cake layer on serving platter. Frost the top of the cake layer (leave the sides plain) with about half the frosting. Spoon half the pie filling onto the frosting; use the handle of a spoon to swirl the pie filling around the frosting. Do not overmix. Top with second cake layer. Repeat frosting and pie filling additions. Chill cake until serving time.
Substitute cream cheese frosting for the vanilla or white frosting.
Chop up any leftover cake and fold into vanilla ice cream for a dessert treat.
Use non-gluten free yellow cake mix instead to make one 8-in. (20-cm) diameter cake.