Cut banana peel into a 1-inch-wide flap down the length of the banana, leaving the skin attached at the bottom. Open the flap and cut a row of notches out of the banana, leaving space between each banana square.
Stuff each space with chocolate chips and a mini marshmallows. Replace flap of banana and wrap in aluminum foil, shiny facing up. Place on coals, leaving the stem side up, and cook for 8-10 minutes. Unwrap and serve.