Slice into the banana and make a slit lengthways. Chop the marshmallows and stuff into the banana along with the chocolate chips (you can use just marshmallow or just chocolate, if liked). Wrap banana in aluminium foil.
Place banana directly over hot coals of a barbecue, or along the outer edge of a campfire. Cook for 5 to 10 minutes. Remove from heat and let cool, then open and enjoy!