Place cookie crumbs in a small bowl and add the melted butter and sugar if using. Stir until all the crumbs are coated. Press into a 11x7-inch oblong pan (UK--a tray bake pan is a good size).
Spread pie filling over crust and top with whipped topping.
Chill at least 4 hours or overnight. Freezing works well too if you want a frozen dessert.
Notes
You can substitute 2 cups of real whipped cream for the whipped topping.