½ cup vegetable oil
½ cup chopped walnuts, if desired
1 can (11 oz) mandarin orange segments, drained (reserve 1/3 cup liquid)
1 can (20 oz) crushed pineapple, undrained
1 box (4-serving size) vanilla instant pudding and pie filling mix
½ to 1 teaspoon grated orange peel, if desired
1 cup frozen whipped topping, thawed
Heat oven to 350°F (325°F for dark or nonstick pan). Grease or lightly spray bottom only of 13x9-inch pan.
In large bowl, beat cake mix, oil, walnuts, orange segments, reserved 1/3 cup orange liquid, and eggs with electric mixer on low speed 30 seconds, then on medium speed 2 minutes. Pour into pan.
Bake 35 to 40 minutes or until toothpick inserted in center comes out clean. Cool completely, about 1 hour.
To make pineapple frosting, stir together pineapple, dry pudding mix and orange peel. Gently stir in whipped topping. Spread on cake. Store tightly covered in refrigerator.