Take aluminum foil and make a boat for your banana to fit into. Next slice the banana down the middle, then add small  marshmallows and chunks of mini chocolate chips.  I bake mine at 350° for about 15 minutes.
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 Nice job!

 Just plain old pealed bananas are good done on the grill, w/o the extra calories (as if anyone is counting).

Nicely done!  I did a dessert like this at a completion in WI in 2011.  Mine was white chocolate and butterscotch chips and whipped cream...