Cut a slit in the banana, lengthwise, but not all the way through to the bottom
Spread open and stuff with marshmallows and chocolate chips
Place on a sheet of tin foil and loosely fold over the ends and top (leave lots of head room so you don't get melted marshmallow all over the top of your tin foil
Grill over medium heat for 3-5 minutes, until the marshmallows are fluffy and the chips are softened and melty
Top with whatever crunchy topping you like- toffee, granola, graham crackers, vanilla wafers, etc.
Notes
Plan on 1/2 to one whole banana per personIf adding peanut butter, spread it on the banana first before adding marshmallows and chocolate