01 - Preheat oven to 350°F. Lightly grease a 9x13-inch baking dish with butter or cooking spray.
02 - Spread the lemon pie filling evenly across the bottom of the prepared dish. Distribute mandarin orange segments over the filling and sprinkle with lemon zest.
03 - Pour the dry yellow cake mix over the fruit layer in an even layer. Do not stir or mix the layers together.
04 - Drizzle melted butter and whole milk evenly over the cake mix, ensuring coverage of as much dry mix as possible. Sprinkle granulated sugar over the top for additional sweetness if desired.
05 - Bake for 35 to 40 minutes until the top is golden brown and the edges are bubbling. The center should appear set.
06 - Allow the cake to cool for at least 15 minutes before serving. Serve warm, optionally topped with whipped cream or vanilla ice cream.