In medium bowl, combine 1 tablespoon vegetable oil, soy sauce, garlic, ginger root and cornstarch. Toss chicken in sauce to coat and marinate 30 minutes. In a wok, heat remaining 2 tablespoons oil and cook peppers and celery over high heat, stirring frequently until softened. Add green onions and cook 2 minutes more. Remove vegetables from wok. Drain chicken and pat dry with paper towels. Add chicken to wok and stir fry until chicken is done, about 3 minutes. Mix remaining ingredients together in a small bowl. Add to chicken with vegetables; simmer 3 minutes.