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