Heat a wok over a high heat, add the oil and once smoking hot add the chicken and stir-fry for a minute. Then add the oyster sauce, sugar and light and dark soy sauce, stirring well to coat the chicken and cook for a further minute or two.
Add the onion, red and green peppers, garlic and ginger and continue to saute for a further 2 minutes. Then add the chicken stock and stir-fry until the chicken is cooked through.
Stir in the spring onion and cashew nuts, ensuring everything is coated with the sauce. Serve immediately with steamed rice or noodles.