Preheat oven to 180 degrees Celsius, fan forced. Place chicken breasts between 2 pieces of baking paper. Using a meat hammer or the end of a rolling pin, bash chicken breasts until 1cm thick.
Place beaten egg in a medium size bowl, and ground hazelnuts on a large plate. Dip each chicken breast into the beaten egg mixture until well coated, then place onto the ground hazelnuts, turning over to cover well.
Place chicken on a baking tray lined with baking paper and bake in the oven for 30-40 minutes, or until chicken has cooked through. Serve with a salad or steamed vegetables.