1. Cut chicken into strips; place in a resealable plastic bag. Add cornstarch and toss to coat. Combine soy sauce, ginger, and garlic powder; add to bag and shake well. Refrigerate for 1-1 ½ hrs.
2. Bring pot of water to boil. Add spaghetti and cook until al dente. Heat 3-4 Tbs. vegetable oil on medium heat. Add chicken and cook until no longer pink. Add onion, carrots, celery, broccoli and additional 1-2 Tbs. vegetable oil as needed. Cover and cook until vegetables are tender. Stir occasionally. Add sauce and spaghetti; cover and simmer for 5 min.