Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.
Spread the crushed pineapple evenly over the bottom of the baking dish, including the juice.
Add the mandarin oranges on top of the pineapple in an even layer.
Sprinkle the dry yellow cake mix evenly over the fruit layer. Do not mix.
Drizzle the melted butter evenly over the cake mix.
For added texture and flavor, sprinkle shredded coconut and chopped pecans on top (optional).
Bake for 45-50 minutes, or until the top is golden brown and the edges are bubbly.
Allow the cake to cool for a few minutes before serving. Serve warm or at room temperature.