Preheat oven to 350℉/177℃.
Spray an 8-inch square pan with cooking spray. Set aside.
In the bowl of a food processor, combine flour, oats, brown sugar, cinnamon, and salt. Pulse to combine.
Add butter slices, a few at a time, pulsing after each addition.
Pulse until combined and crumbly.
Place ⅔ of the mixture into the prepared pan, and press evenly across the bottom.
Bake for 15 minutes, or until just starting to brown.
Remove oat base from the oven and top with apple pie filling and the remaining crumble mixture.
Return to the oven and bake 40 minutes, or until lightly browned.