Rinse chicken and pat dry with paper towels. Cut chicken into 1 inch pieces. Combine sugar, cornstarch, and mustard in a small bowl. Add soy sauce, water, and vinegar to cornstarch mixture; stir until smooth. Set aside. Heat the wok over medium heat until hot. Drizzle 1 tablespoon of oil into the wok and heat for 30 seconds. Add chicken and garlic; stir fry 5 to 6 minutes or until chicken is no longer pink in the center. Remove chicken to a large bowl. Drizzle remaining 1 tablespoon of oil into the wok. Add red pepper, celery, and onion; stir fry 3 minutes or until vegetables are crisp tender. Stir soy sauce mixture; add to the wok. Stir fry 30 seconds or until sauce boils and thickens. Return chicken and any accumulated juices to the wok; heat through. Serve with noodles Garnish is desired.