Preheat oven to 350 degrees.
Spray a 9 x 13 pan with cooking spray.
In a large bowl, combine cake mix, eggs, oil, and 1 can of crushed pineapple with the juice (or half of a large can) and mix well.
Pour into prepared baking pan and bake for 25 – 30 minutes, or until toothpick inserted in center of cake comes out clean.
Cool completely on a wire rack.
In a medium sized bowl, fold together whipped topping, a 3oz box of vanilla pudding, and 1 can crushed pineapple or pineapple tidbits with the juice (or other half of can if using a 16oz can). Spread over the top of the cooled cake.
Gently spread the whipped topping over the entire cake, smoothing it out evenly.
Refrigerate the cake for at least one hour before serving to allow the flavors to meld together.
Slice and serve chilled for a light and refreshing dessert.