Cut off stem and end of banana, cut both peel and banana length wise on the inside curve- making sure not to cut completely through the back. Open and lay on a sheet of foil.
Sprinkle chocolate chips down the center of banana, followed by marshmallows.
Wrap in foil and roll edges to secure.
Place on grill, cook 3 minutes per side or until chocolate is melted, marshmallows are soft, and banana is warmed through.
Open foil, remove banana peel, transfer to serving dish.