Mix broth, soy, sherry, cornstarch, and sesame oil to blend; set aside. Mix chicken with garlic and chilies. In a wok or 12-inch frying pan over high heat, heat 2 teaspoons oil unitl hot. Add half the chicken mixture; stir-fry until chicken has golden brown tinge and is no longer pink in thickest part (cut to test), about 3 minutes; remove to a dish. Repeat with remaining chicken, adding oil as needed. Return cooked chicken to wok; stir in reserved sauce, onion pieces, and nuts. Cook, stirring, until sauce bubbles and thickens, about 1 minute. Serve with rice; add onion garnish. Serves 4.