Preheat oven to 350 degrees.

Spray a 9 x13 pan with non-stick cooking spray. Add both cans of pie filling to the dish and spread out so that it evenly covers the bottom of the dish.

Spread dry cake mix in an evenly layer over the pie filling, then place slices of butter over the cake mix.

In a bowl, mix together the oat and brown sugar. Then sprinkle over the cake.

Bake at 350 degrees until bubbly and golden brown.

Allow to cool slightly. Serve warm and with vanilla ice cream if desired.