HEAT oven to 350°F.
BEAT cake mix, dry pudding mix, 1 cup sour cream, water, oil, eggs and orange zest in large bowl with mixer on low speed 1 min.; scrape bowl. Beat on medium speed 2 min. Pour into 2 greased and floured 9-inch round pans.
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 remaining sour cream and powdered sugar in large bowl with whisk until well blended. Stir in COOL WHIP.
STACK cake layers on plate, filling layers with half each of the COOL WHIP mixture and oranges. Frost top with remaining COOL WHIP mixture. Garnish with remaining oranges. Keep refrigerated.