Using a sharp knife, cut the chicken into bite-sized chunks.
Trim and chop the green onions.
Peel the ginger and cut into thin matchsticks.
Seed the peppers and cut the flesh into bite-sized chunks.
Heat the oil in a wok or large skillet until almost smoking.
Add the green onions and ginger.
Stir-fry over a high heat for 1 minute.
Add the cashew nuts and chicken.
Stir-fry for 3 minutes, or until chicken is tender.
Add the green peppers and stir-fry for 3 minutes.
In a small bowl, stir together the soy sauce, sherry, and cornstarch.
Add to the skillet and stir-fry until the chicken is cooked through and the sauce thickens slightly, 2 to 3 minutes.
Season with black pepper and serve.