PLACE cake on serving plate. Use long serrated knife to cut 3/4-inch-thick horizontal slice from top of cake; set aside. Cut 1-inch-wide and 1-inch-deep tunnel around centre of interior of cake with short serrated knife, being careful to not cut through to bottom of cake. Remove cake cutout; reserve for snacking.
ADD boiling water to jelly powder in medium bowl; stir 2 min. until completely dissolved. Add enough cold water to ice cubes to measure 3/4 cup. Add to jelly; stir until ice is completely melted. Remove 1/2 cup jelly; place in separate medium bowl. Add Cool Whip; stir with whisk until well blended. Refrigerate 10 min. or until thickened to spreading consistency.
MEANWHILE, refrigerate remaining plain jelly 5 to 10 min. or until thickened. Stir in 1/4 cup each strawberries, raspberries and lime zest; spoon into tunnel of cake. Replace cake top. Frost cake with thickened jelly mixture. Garnish with remaining berries. Refrigerate 2 hours.
serving size = 1 piece (72 g)