Preheat oven to 350°F. Grease a 9x13 baking dish with nonstick spray.
Pour the peach pie filling into the prepared baking dish and spread in an even layer.
Sprinkle the dry cake mix evenly over the top of the peaches.
Cut the butter into thin slices and arrange over the top of the cake mix.
Bake for 50-60 minutes until golden brown on top.
Remove from oven and let cool for 10 minutes before serving warm.
Top with vanilla ice cream or whipped cream if desired.