Preheat oven or grill.

Prepare a piece of foil large enough to wrap the banana and spray with cooking spray.

Cut the stem off of the banana.

Slice the banana lengthwise through the skin, about 3/4 of the way through, being careful not to cut all the way through.

Open the banana slightly to create a pocket.

Cut the chocolate into small pieces.

Place the chocolate pieces into the banana pocket.

Add the marshmallows on top of the chocolate.

Wrap the banana tightly in the foil.

Place the wrapped banana in the oven or under the grill.

If grilling, cook for 10-15 minutes, or if baking, cook for 15-20 minutes, until the chocolate and marshmallows are melted.

Remove from the oven or grill and let rest for a few minutes before unwrapping.

Enjoy directly from the foil or transfer to a plate.