Preheat oven to 350 degrees and spray a 9x13-inch baking pan with baking spray with flour.
Use a hand-held electric mixer to beat cake mix, 5 tablespoons of butter, and 1 cup of oats until crumbly.Measure out 1 cup and set it aside.
Add egg to the remaining mixture in the mixing bowl and beat it in.
Press mixture evenly into the bottom of the prepared baking dish.
Spread peach pie filling on top.
In the same mixing bowl, combine the 1 cup of reserved cake mixture with the remaining butter, oats and the brown sugar. Beat together and then sprinkle evenly on top of the peaches.
Bake for 30 to 35 minutes or until light brown on top. Let cool before slicing.