Crush Oreos in a food processor to a very fine texture. Place crushed Oreos in a large resealable plastic bag and add melted butter. Shake to mix until well combined.
Press buttered crumbs into the bottom of a 9-x-13-inch baking dish, making sure to cover the entire bottom.
In a medium bowl, blend powdered sugar, cream cheese, butter, and half of the whipped topping with a hand mixer.
Blend well and pour over crust.
In another bowl, combine instant pudding and milk. Whisk together until pudding thickens, then pour over the cream cheese layer. Refrigerate for at least 5 minutes.
Top off with the remaining whipped topping and refrigerate at least 1 hour before serving. Add lemon slices for garnish.