Preheat the oven to 200 degrees C. Place the Parmesan on a sheet of greaseproof paper and the breadcrumbs on another sheet. Beat the egg white in a shallow bowl with 2 tablespoons water. Dip the chicken into the Parmesan, then into the egg whites and then into the breadcrumbs.
Heat the oil over moderate heat in a large nonstick frying pan. Cook the chicken for 3 minutes each side. Transfer to a baking tray and sprinkle with the mozzarella; spoon the tomato sauce on top. Bake for 10 minutes or until the chicken is cooked through.