Heat oil in large nonstick skillet over medium heat. Add chicken; cook 5 minutes. Turn chicken; cook 5 minutes. Remove and reserve.
Pour off all but 1 Tbl drippings. Cook chopped onion and garlic in drippings 6 minutes or until browned and tender, stirring occasionally. Add broth and sherry; bring to a boil. Blend soy sauce into cornstarch in cup until smooth. Stir into broth mixture. Return chicken to skillet; add mushrooms.
Reduce heat to medium-low. Cover and simmer 20 minutes or until chicken is cooked through.
Serve chicken and sauce over noodles. Sprinkle with green onions. Garnish with pepper strips and green onions, if desired.