Spread the apple pie filling onto the bottom of a 9-inch pie plate.

In a medium bowl, whisk together the brown sugar, oats, and nuts, if using.

Pour the melted butter over the oat mixture. Mix everything together until well moistened and a bit crumbly.

Crumble the oat topping over the apple filling and spread evenly.

Bake in the preheated oven for 35 minutes or until filling is bubbly and the crisp topping is a golden brown.

Cool for a few minutes on a wire rack before serving warm or let cool completely and serve at room temperature.