Light a grill. Spread 4 graham crackers with the Nutella; spread the remaining 4 with marshmallow fluff. Press the bananas onto the Nutella and sprinkle with the hazelnuts. Sandwich the graham crackers together. Wrap them in the parchment paper and then in foil.
Grill the s'mores over moderate heat for about 10 minutes, turning once or twice, until the marshmallow fluff is gooey and lightly toasted. Remove the foil, peel back the parchment and serve.