Crush the graham crackers in a resealable bag with a rolling pin, or in a food processor, if not already crushed. Transfer to a medium mixing bowl and set aside.
In a small microwave safe dish, melt the butter and sugar together. Stir to dissolve completely. Pour over the graham cracker crumbs and combine thoroughly. Firmly press the crumbs into a 13×9-inch pan.
In a stand mixer or with a hand-held blender, beat the cream cheese, pudding mix, milk and lemon zest until well combined. Pour onto prepared crust and smooth into an even layer.
Add the whipped topping in an even layer and garnish with additional graham cracker crumbs and lemon slices. Refrigerate for at least 4 hours or until set.