Preheat the grill to medium-high heat and lightly grease the grates.
Place the banana slices onto the grill and brush with melted butter or oil.
Grill for 2 minutes on each side until lightly caramelized and golden brown.
Meanwhile, make the sauce by combining the dark chocolate, hazelnut butter, heavy cream, and a pinch of sea salt in a small pot.
Heat over low heat, stirring constantly until smooth and creamy
Serve the grilled bananas warm with a drizzle of the chocolate-hazelnut sauce and garnish with toasted hazelnuts.