Combine all the ingredients for the sauce and set the mixture aside.
Heat 1 tablespoon of the groundnut oil in a wok over a high heat until the oil starts to shimmer. Season the chicken with salt and tip half of it into the wok. Stir-fry for 2–3 minutes, until golden, then remove the chicken using a slotted spoon and set aside. Heat the remaining oil and stir-fry the rest of the chicken in the same way. Remove and set aside.
Add the cashews and red peppers to the wok and stir-fry for 1 minute. Add the garlic and spring onions and cook, stirring, for a further minute. Return the chicken to the wok and pour in the sauce. Cook for 3–4 minutes until the chicken is cooked through and the pepper is tender.