Carefully add each can of apple pie filling to the dish, then smooth with a spatula to fill the dish evenly.
Sprinkle the cinnamon and walnuts over top of the pie filling.
In a small bowl, combine cake mix and melted butter. Stir with a fork to combine. It should form a crumbly mixture.
Spread the cake mix mixture over the top of the apple layer.
Bake for 45 minutes or until the top of the cake mix is golden brown.
Remove from the oven and allow it to rest for at least 10 minutes.
Notes
You can also spread the cake mix over the apples dry, then drizzle the melted butter over the top of it before baking.DIY Pumpkin Pie Spice: If you don't have pumpkin pie spice but you'd like to use it, make your own! Just combine a scant teaspoon of cinnamon with one pinch each of nutmeg, ground cloves, and ginger. If you have allspice, add a pinch of that as well!