HEAT oven to 350°F.
PREPARE cake batter as directed on package; stir in carrots, pineapple and 3/4 cup nuts. Pour into 2 (9-inch) square pans sprayed with cooking spray.
BAKE 25 to 30 min. or until toothpick inserted in centers comes out clean. Cool cakes in pans 10 min. Invert onto wire racks; gently remove pans. Cool cakes completely.
BEAT cream cheese and sugar in large bowl until blended. Whisk in COOL WHIP.
STACK cake layers on plate, spreading frosting between layers and on top and sides of cake. Sprinkle with remaining nuts.