1.Cut chicken into thin strips; coat with 1 Tbsp. cornstarch.
2.Stir-fry with onion and garlic in hot oil 3 minutes. Add frozen vegetables; stir-fry 2 to 3 minutes until heated.
3.Combine 2/3 cup water, soy sauce and 4 teaspoons cornstarch; stir into chicken mixture. Cook, stirring, until sauce boils and thickens.
4.Add vermicelli; toss to combine.