Wash the asparagus and trim off any woody ends. Cut the stems diagonally into 4cm lengths. Wash the spring onions and cut into 3cm lengths.
Wash and deseed the peppers, then cut into fine strips. Peel and crush the garlic into a bowl. Add the soy sauce and sugar and stir until the sugar has dissolved.
Cut the chicken breast into strips and season with salt and black pepper. Heat the oil in a wok or large frying pan over a high heat. Add the chicken and stir-fry until golden. Remove the chicken to a plate and drain off the excess oil.
Stir-fry the vegetables in the wok for 2 minutes until evenly cooked.
Add the sauce mixture to the wok, bring to the boil and simmer for about 1 minute.
Chop the chilli and add the wok with the cashew nuts and chicken strips. Stir-fry for 2 minutes. Serve with rice if desired.