A few hours ahead of making these ice cream sandwiches (or the night before), slice your bananas and freeze them.
When ready to assemble ice cream sandwiches, line a cookie sheet with wax paper. Set out your cookies. Place sprinkles on a plate or in a shallow bowl.
Place frozen bananas in a Yonanas dessert maker and process to make ice cream. If you don't have a Yonanas, you can use a food processor. (If you're using a food processor, the mixture may end up too soft. If it won't hold up to scooping, freeze it for awhile before making your ice cream sandwiches.)
Scoop one tablespoon of frozen banana "ice cream" on half of the cookies. Top with the remaining cookies. Roll in sprinkles.
Place back on cookie sheet and freeze for about an hour, then you can place them in a ziploc bag for storing in the freezer.