Cook spaghetti according to package directions; drain. Toss with 1 tablespoon sesame oil; set aside. In a small bowl, combine the cornstarch, broth, soy sauce and vinegar until smooth; set aside.
In a large skillet, stir-fry the chicken, mushrooms, red pepper and garlic in remaining oil for 5-8 minutes or until chicken juices run clear. Stir broth mixture and add to skillet. Bring to a boil; cook and stir for 2 minutes or until thickened. Add spinach; cover and cook for 2-3 minutes or until spinach wilts. Add the onions, sherry, ginger and spaghetti; cook for 2-3 minutes or until heated through. Sprinkle with sesame seeds.