Preheat oven to 350°F. Lightly grease a 9×13 baking dish and set aside. In a large mixing bowl, beat together crushed pineapple (juices included) and the dry cake mix.
Beat until fluffy and fully combined (1-2 minutes).
Transfer the cake batter to the baking dish, spreading evenly.
Bake for 25-30 minutes, until the cake is golden brown. The cake is so light, it may wobble just slightly, but should not have raw batter inside. You can test with a toothpick to ensure just a few crumbs stick to the toothpick and there is no wet batter. Remove from oven and allow to cool completely.
Whip heavy cream until soft peaks form. Add powdered sugar and continue whipping until whipped cream has stiff peaks.
Spread whipped cream over the cooled cake. Garnish with pineapple slices. Slice into pieces and serve.