TOSS strawberries with sugar; let stand 10 min. or until sugar is dissolved.
MEANWHILE, cut each cake slice diagonally in half. Place 1 cake piece on each of 12 dessert dishes.
BEAT pudding mix and milk with whisk in medium bowl 2 min. Gently stir in half the COOL WHIP.
SPOON 2 Tbsp. strawberries over each cake piece; top with 1/4 cup pudding and second cake piece. Cover with remaining strawberries and remaining COOL WHIP. Serve immediately or cover and refrigerate until ready to serve.