Preheat the oven to 350°F (175°C). Grease a 9×13-inch baking dish.

Layer the fruit: Spread the drained pineapple chunks evenly over the bottom of the prepared baking dish. Optionally, you can add sliced peaches around the pineapple.

Sprinkle the cake mix: Evenly sprinkle the dry yellow cake mix over the fruit layer. Do not mix.

Add the butter and sugar: Drizzle the melted butter evenly over the cake mix. Then sprinkle the brown sugar on top.

Add nuts (optional): Sprinkle chopped pecans or walnuts on top for added crunch and flavor.

Bake: Bake for 40-45 minutes, or until the top is golden brown and the cake is fully cooked (you can insert a toothpick to check the cake layer).

Cool and serve: Allow the cake to cool for a few minutes before flipping it onto a serving plate. Spoon any remaining fruit and syrup from the pan over the top. Serve warm.