We make these camping and the kids love them.  DW found the recipe at taste of home.
[Image Can Not Be Found]

Prep/Total Time: 20 min.
Yield: 4 Servings

Ingredients
4 medium unpeeled ripe bananas
4 teaspoons miniature chocolate chips
4 tablespoons miniature marshmallows

Directions
Cut banana peel lengthwise about 1/2 in. deep, leaving 1/2 in. at both ends. Open peel wider to form a pocket. Fill each with 1 teaspoon chocolate chips and 1 tablespoon marshmallows. Crimp and shape four pieces of heavy-duty foil (about 12 in. square) around bananas, forming boats.
Grill, covered, over medium heat for 5-10 minutes or until marshmallows melt and are golden brown.

Tip - Banana Basics
Look for plump bananas that are evenly yellow-colored. Green bananas are under-ripe, while a flecking of brown flecks indicates ripeness. If bananas are too green, place in a paper bag until ripe. Adding an apple to the bag will speed the process. Store ripe bananas at room temperature. To prevent bruises, a banana hook or hanger is a great inexpensive investment. For longer storage, you can place ripe bananas in a tightly sealed plastic bag and refrigerate. The peel will become brown but the flesh will remain unchanged. One pound of bananas equals about 3 medium or 1-1/3 cups mashed.