Chicken-Vegetable Lo Mein
["water", "3 Tbsp. cornstarch, divided", "2 Tbsp. soy sauce, divided", "1 chicken breast (1/2 lb.), skinned, boned and sliced thin", "1 tsp. sugar", "4 Tbsp. oil, divided", "1 clove garlic, minced", "1/2 c. sliced onion", "2 c. sliced celery", "2 c. cabbage or celery cabbage", "3 c. bean sprouts", "1/2 c. sliced water chestnuts", "1/2 c. sliced bamboo shoots", "4 oz. sliced mushrooms", "1/4 lb. spaghetti, broken in fourths, cooked"]
["In medium bowl, combine 2 tablespoons water, 1 tablespoon cornstarch and 1 tablespoon soy sauce.", "Add chicken and toss until coated; set aside.", "In small bowl, mix 1/2 cup water, remaining 2 tablespoons cornstarch, remaining 1 tablespoon soy sauce and the sugar; set aside."]
["water", "cornstarch", "soy sauce", "chicken", "sugar", "oil", "clove garlic", "onion", "celery", "cabbage", "bean sprouts", "water chestnuts", "bamboo shoots", "mushrooms"]