Slice banana into 12, 1/2" pieces. Line a small baking sheet with parchment paper.
Assemble bites: Place 6 banana slices on baking sheet and top with a large dollop of Marshmallow Fluff and a sprinkle of graham cracker crumbs. Top with remaining bananas to make a sandwich. Stabilize with a toothpick if desired. Freeze until firm, 1 hour.
Once sandwiches are frozen solid, dunk half in melted chocolate, and then into remaining graham cracker crumbs. Place back in freezer until fully set, 30 minutes more (or until ready to serve).