Mix the cornflour, 1 tablespoon oil and salt and marinate the chicken thighs for a few minutes.
Heat the remaining oil in a wok and slightly stir-fry the chicken and soy sauce, then remove and set aside. Add the garlic and stir-fry until fragrant, then add the onion and green capsicum. Add the chicken and stir-fry until chicken is done. Season with chicken stock powder and serve.