In a small heavy skillet, cook and stir the hazelnuts over medium heat until toasted, about 4 minutes. Sprinkle with sugar; cook and stir for 2-4 minutes or until sugar is melted. Spread on foil to cool.
In a small saucepan, melt chocolate chips with cream over low heat; stir until smooth. Remove from the heat; cool to room temperature. In a small mixing bowl, beat cream cheese and brown sugar until blended. Beat in yogurt and vanilla; fold in whipped topping.
In two parfait glasses, layer the graham crackers, yogurt mixture, chocolate mixture and hazelnuts. Refrigerate until chilled. Garnish with chocolate curls and whipped topping if desired.