Cook rice noodles according to package directions.
Meanwhile, in a small bowl, combine the soy sauce, cornstarch and garlic. Add chicken. In a large cast-iron or other heavy skillet, saute chicken mixture in peanut and sesame oils until no longer pink. Add onions; cook 1 minute longer.
Drain noodles; stir into skillet. Add cashews and chili sauce and heat through. If desired, top with toasted sesame seeds.