• Preheat oven to 350 degrees. 
• Grease a 13x9 inch baking pan or two 8" cake pans.
• In a large mixing bowl, combine the boxed yellow cake mix, eggs and oil.
• Beat on low speed until smooth. Drain the mandarin oranges (reserving the juice) and add them to the mixer. Gradually add the some of the  juice from the can until your cake batter is thin enough to pour but not runny.
• Beat on low until well incorporated and the oranges have broken up slightly.
• Pour into the prepared pans, bake at 350 degrees for 30 to 40 minutes or until tests done with a toothpick.  
• Remove from oven and cool for 5 minutes.
• Run a knife around the edge of the pan and turn the cakes out onto a cooling rack. If doing a sheet cake you can just leave it in the pan.

For the topping:

• Put the thawed Cool Whip in a large mixing bowl. Add the vanilla pudding mix. Stir and let sit for 5-10 minutes.
• Add the drained crushed pineapple and stir until well incorporated. It the topping seems too thick, thin it down with the reserved pineapple juice.
• You can make your cake four layers by cutting them with a serrated knife and frosting between the layers and on top. You can place the topping directly on the cake if you used a baking dish. Refrigerate overnight, covered.
• You can serve the cake as-is or you can decorate it to your heart's content. I made a small batch of orange buttercream icing and piped some trim on mine and garnished with orange segments and mint leaves.