Step 1 Heat a large wok over high heat. Once the wok is hot, add 1 tablespoon of the oil and carefully swirl around to coat the side of the wok. Heat until very hot.
Step 2 It is important to heat the wok before adding the oil, otherwise the oil can end up overheating and burning. You will know if the oil is hot enough if the beef starts to sizzle when added to the wok.
Step 3 Add one-third of the beef strips and stir-fry for 1-2 minutes or until the beef is browned and just cooked. Transfer to a plate. Repeat with the beef in two more batches, reheating the wok between each batch. Remove all beef from the wok.
Step 4 Adding and cooking the beef in batches is very important as it seals the meat, keeping in the juices. If you add too much meat at once, the wok will lose its heat and the meat will stew and become tough.
Step 5 Heat remaining oil in the wok over medium-high heat. Add the onion, capsicum, broccollini, corn and garlic. Stir-fry for 2 minutes. Add the water, cover and cook for 30-60 seconds or until the vegetables are just tender.
Step 6 Add the oyster sauce and soy sauce to the wok. Toss well to combine. Add the beef and toss until heated through. Serve immediately with rice.