Divide the broccoli into florets, wash and drain. Peel the stalk and cut it into pieces about 1cm thick.
Blanch the broccoli in boiling salted water for 2 minutes, drain and cool under cold water. Drain again.
Chop the walnuts.
Peel and finely dice the onions and garlic. Peel and finely grate the ginger.
Cut the chicken breast fillet into small pieces. Mix with the soy sauce and cornflour.
Heat the oil in a wok or pan and fry the chicken over a high heat for 2 minutes. Remove and set aside.
Add the onions and broccoli to the wok and stir-fry for 2 minutes.
Add the nuts, garlic and ginger, and stir-fry for 1 minute.
Mix the oyster sauce with 4 tbsp water, add to the vegetables and bring everything to the boil.
Return the chicken to the wok and cook for 2 minutes. Season with salt and pepper and spice up with a little sambal, if desired. Serve with rice.