Slice the beef thinly and cut the vegetables into even pieces so they cook through at the same time.
For the dressing, combine oyster sauce, soy sauce, sugar and cornstarch. Mix to dissolve and set aside.
Place wok over high heat, add a little oil and cook the beef in 3 batches; set aside when cooking and loosely cover with aluminium foil.
Add remaining oil to the wok and cook onion for 1 minute; add carrots, capsicum and beans and cook for 2 minutes. Add bok choy and stir until slightly wilted, then return the beef to the pan and add dressing. Serve with coriander.
Notes & Tips
Prepare all your ingredients in advance to make cooking easy.