It doesn't get any easier than this. Consider this your new go-to 4-ingredient dessert recipe.
Coat inside of a slow cooker with nonstick cooking spray.
Pour pie filling into Crock-Pot slow cooker.
Combine cake mix and butter in medium bowl. Spread evenly over pie filling. Sprinkle with walnuts.
Cover; cook on LOW 3 to 4 hours or on HIGH 1 1/2 to 2 hours.