Coat a 9″ x 13″ pan with cooking spray. Stir together graham cracker crumbs, ground walnuts, and butter until incorporated.
Press the mixture into the pan and chill in refrigerator while preparing other ingredients.
Beat together cream cheese and powdered sugar until smooth..
Fold in half of the whipped topping.
Spread evenly over the chilled crust and set aside.
Beat packages of lemon pudding mix with 3 cups of milk for 2 minutes or until mixture starts to thicken.
Spread the pudding mixture evenly over the cream cheese layer. Chill for at least an hour.
Spread the other half of the whipped topping over the pudding layer.
Add chopped walnuts to the top of the whipped topping layer.
Serve and refrigerate leftovers.