Preheat oven to 350°F. Lightly grease a 9x13 inch baking dish.
Spread the crushed pineapple (with all its juice) evenly across the bottom of the baking dish.
Spoon the cherry pie filling evenly over the pineapple layer.
Sprinkle the dry cake mix evenly over the fruit layers. Do NOT stir — just spread it dry and flat.
Pour the melted butter evenly over the entire surface of the dry cake mix, trying to cover as much as possible. Sprinkle with nuts if using.
Bake for 45-55 minutes until the top is golden brown and the edges are bubbling. Let cool 10 minutes before serving. Serve warm with vanilla ice cream.
Notes
Do not stir once you add the cake mix — that is the whole point of a dump cake! Make sure the butter covers the dry mix as evenly as possible to avoid dry patches on top. Serve warm for best results. Try with coconut cake mix for a tropical twist.