Preheat the oven to 375°F. Lightly spritz the bottom and 1-inch up the side of a 13 x 9-inch baking dish with cooking spray. Set aside.
In a mixing bowl using a fork sift together the cake mix, 1/2 cup oats and chopped nuts.
Add the melted butter and egg. Mix until fully moistened. Remove 1 cup mixture to a separate bowl.
Press the remaining dough onto the bottom of the dish. Bake for 15 minutes.
While the bottom crust is baking add the remaining 1/4 cup oats to the reserved dough. Mix just until incorporated and crumbly.
After 15 minutes remove from the oven and spread the pie filling over the crust. Sprinkle with the crumb topping.
Bake for an additional 15-20 minutes or until lightly golden.
Cut into 16 squares or 32 triangles and serve warm with ice cream or at room temperature.
Store tightly sealed chilled or at room temperature.