Freeze the banana slices on a plate for at least two hours.
Use a food processor or blender (blender works better) to blend the bananas until smooth.
Place half of the cookies face-down on a large serving dish. Fill with the banana "ice cream" and top with another cookie. Repeat until all the sandwiches are assembled.
If topping with chocolate and caramel sauce: Using a spoon, drizzle the chocolate sauce in a zig zag pattern on the cookies. Turn the serving dish 90 degrees and drizzle the caramel sauce over the sandwiches. Place into the freezer for at least 30 minutes and serve.
If topping using powdered sugar: Liberally dust with powdered sugar just prior to serving.