To serve 2-3, you'll want:
2 tbsp natural peanut (or other nut) butter
chopped nuts (I used walnuts)
shaved or chopped dark chocolate or cacao nibs
sprinkle of sea salt
drizzle of honey (optional)
Slice your banana in half, but not all the way through. Spread with PB and sprinkle with goodies.
Wrap it up, folding banana halves together, and cook over hot coals until banana is soft and cooked. Time will depend on your coals. I had to rotate my banana (with tongs) and unwrap/re-wrap it a few times until it was just right.
Eat hot, with spoons (or pretzels!).