Preheat oven to 375°. Prepare pie crust according to directions and pat it into the bottom of a 9×13 pan.
In large mixing bowl, combine apple slices, sugar, lemon juice and cinnamon. Spread in an even layer over crust.
In the food processor, combine the flour, butter, and brown sugar, pulsing until coarse crumbs are formed, or in a large mixing bowl, combine these ingredients, cutting butter into sugar and flour with a pastry blender or two knives held together. Stir in nuts. Sprinkle crumb top over apple layer.
Bake for 45 minutes to an hour or until filling bubbles. Cool completely.
If preparing ahead of time to freeze. Wrap with foil and label prior to baking and freeze. Then, when ready to serve, bake the frozen pie at 425° for 15 minutes. Reduce heat to 375° and continue baking as directed.