Next, evenly sprinkle out the cake mix on top of the fruit. Cover the whole dish and spread it out until it's even. Gently pat the powder down into the liquid from the fruit.
Lastly, the most important step is to take your melted butter and pour it all over the top of the cake mix. Make sure all of the cake mix powder is wet from either the fruit or the butter, pat it all down so that it spreads.
Place it in the oven and bake for 30-35 minutes. It's finished when a fork in the center comes out with only a few crumbs.
While the cake is baking, you can decide to brown pineapple slices in the oven to create more of the “pineapple upside-down cake” look – totally optional! Line a baking sheet with aluminum foil, spread the slices out, rub the brown sugar on top of the slices. Bake in the oven for 20 minutes.
When the cake is finished, you can eat it warm just like a crumble. If you want to top off the whole cake with cool whip, let it fully cool to room temp. Then spread cool whip all over, arrange your pineapple slices, and top it all off with lime zest.