Make long slits along the length of the bananas and place each on a large square of foil, open up the slits and press in the chocolate chips and marshmallows. Wrap up the foil loosely to seal. Place on a BBQ or griddle pan and cook for 15 minutes until the bananas are soft and the chocolate has melted.
Meanwhile, mix together the Walnuts and caramel sauce. Open up the foil parcels and top the bananas with the Walnut mixture.
