1.Toss the chicken with the soy sauce in a medium mixing bowl and marinate for 30 minutes.
2.For the sauce, whisk together the lemon zest and juice with the sugar, water and 2 tsp. cornstarch in a small saucepan. Bring to a boil, whisking constantly until thickened (about 4 minutes), then keep warm.
3.Heat the oil in a large skillet. Whisk together the egg, cornstarch, salt and pepper in a small bowl to make a batter. Toss the chicken in the batter and fry for three to four minutes on each side until golden and cooked through.
4.Plate the chicken and spoon the sauce over top. Serve with rice if desired.