Add the juice from the oranges and the orange zest to the cake mix.
Stir to combine.
Bake in a bundt pan at 350 degrees for about 30 minutes.
Cool completly. Frost with Cool Whip and decorate with the mandarin oranges.
I used 3 Tbs. orange zest, but that is just a personal preference. You can also add half the caan of oranges into the batter before baking, but for some reason it always makes my cake stick to the pan. So just experiment. It is just as good with the oranges on top of the cake instead of in it.