Heat the oil in a large wok or frying pan and cook the chicken for 3–4 minutes over a medium-high heat, until golden. Using a slotted spoon, transfer to a plate and set aside.
Return the pan to the heat and add the broccoli, red pepper and spring onions. Stir-fry for 3–4 minutes, until softened.
Meanwhile, place a small pan over a medium-low heat and toast the cashew nuts for 3–4 minutes, shaking the pan occasionally, until golden. Remove from the heat.
Dissolve the cornflour in a small bowl with 1 tablespoon of the water, then mix in the remaining water plus the lemon juice, honey and soy sauce. Add to the vegetables along with the cashew nuts. Reduce the heat to medium-low and return the chicken to the pan. Simmer for 2–3 minutes, until the chicken is cooked through and the sauce hot and thickened. Serve immediately, with steamed rice or noodles, if desired.