Remove foil lid from cake package. (Do not remove cake from pan.) Pierce cake with skewer at 1/2-inch intervals, poking skewer through cake to bottom of pan.
Add boiling water to jelly powder in small bowl; stir 2 min. until completely dissolved. Stir in cold water; pour over cake. Refrigerate 1 hour. Meanwhile, make curls from chocolate. (See tip.)
Invert cake onto platter; cut horizontally in half. Spread bottom half of cake with 1/3 cup Cool Whip; cover with 1 cup pie filling and top cake layer. Frost top and sides of cake with remaining Cool Whip. Garnish with remaining pie filling and chocolate curls.