Preheat oven to 350 degrees. Grease and flour a 13x9" baking dish.
In a large bowl, combine. the cake mix, oil, eggs, and undrained mandarin oranges. Beat together with mixer just until blended. Pour into prepared baking dish.
Bake in a preheated oven for 30-35 minutes, or until a toothpick inserted in the center comes out clean when tested. Place dish on rack to cool completely (several hours.)
For the icing, combine instant pudding, pineapple with juice, and whipped topping and mix by hand until blended. Spread on cooled cake. Serve immediately or refrigerate. Makes 12 to 15 servings. Refrigerate leftovers if there are any. Enjoy!
Note: You can try other flavors of pudding mixing, including vanilla, lemon, or banana.