In a small bowl, combine the banana, sugar and walnuts. Using a pastry brush, lightly brush the edges of each won ton wrapper. Put about a teaspoon of the chocolate-hazelnut spread in the center of each wrapper and top with 1 to 2 teaspoons of the banana mixture. Fold 1 corner of each won ton wrapper diagonally over the filling to form a triangle. Press the edges together to seal and refrigerate for 15 minutes.
Fill a large heavy-bottomed saucepan with about 3/4-inch oil. Heat over medium heat until a deep-frying thermometer inserted in the oil reaches 375 degrees F. (If you dont have a thermometer, a cube of bread will brown in about 2 minutes.) Fry the ravioli, 2 or 3 at a time, turning occasionally, until golden, about 60 to 70 seconds. Drain on paper towels. Cool for 2 minutes and serve warm.