Preheat oven to 350 degrees Fahrenheit.

Prepare yellow cake batter according to package directions.

Beat in the drained mandarin oranges until well combined.

Pour batter into a greased and floured sheet cake pan or two prepared 9-inch round baking pans.

Bake for 22 to 25 minutes, or until a toothpick inserted into the center comes out clean.

Cool in the pan for 10 minutes.

Transfer cake to a wire rack to cool completely. For sheet cake, ensure it is completely cooled before frosting.

In a bowl, combine the drained vanilla instant pudding mix.

Fold in the Cool Whip.

For Sheet Cake: Spread frosting evenly over the top of the cooled cake.

For Round Cake: Spread frosting on top of one layer.

Place the second layer on top of the frosting.

Spread the remaining frosting on the top and sides of the cake.

Garnish with additional mandarin oranges or pineapple chunks, if desired.