Line a 9x9x3-inch baking pan with parchment paper.
In a medium bowl, combine about ⅔ of the chopped Oreos with the whipped topping until just combined. Set aside. Reserve the remaining Oreos.
Place half of the ice cream sandwiches in an even layer in the baking dish. You will need to cut a couple of the ice cream sandwiches to fit them snugly into the dish.
Evenly spread half of the fudge sauce onto the ice cream sandwiches. Follow with a layer of Oreo whipped topping. Repeat layers. Sprinkle the top of the cake with the remaining chopped Oreos. Cover and freeze for at least 3 hours.