1. Heat a grill or grill pan. Using a sharp paring knife, make a lengthwise slit down one side of each banana, slicing through the peel but not the flesh and leaving the ends intact. Loosen peel slightly with your fingers, and stuff each banana with 1/4 cup marshmallows and 1 ounce chocolate. Press peel together gently to enclose filling completely, and wrap bananas in foil.

2. Using tongs, place bananas on grill; cook, turning occasionally, until they are softened and filling has slightly melted, 5 to 7 minutes, depending on ripeness of bananas. Remove bananas from grill, and let cool slightly before carefully removing foil. Serve.