Heat the oven to 350°F and coat a 9-by-13-inch baking dish with cooking spray.
Spread the apple pie filling evenly in the dish and sprinkle it with cinnamon.
Shake the dry cake mix in an even layer over the apples without stirring the layers together.
Scatter the pecans over the mix and cover the surface as evenly as possible with the thin butter slices.
Bake uncovered for 45 to 50 minutes, until the apple filling bubbles vigorously at the edges and the topping is golden with no broad dry patches.
Rest for 20 minutes before scooping so the fruit thickens.