Give the pan a good wipe, return to HIGH heat. When hot, swirl in cooking oil. Add in the beef and onion to the pan, use your spatula to spread out the ingredients all over the pan. Let cook, undisturbed for 15-30 seconds, until the edges of the beef turn brown, but is still red in the middle. Toss and flip the beef and onions, stir fry until cooked to your liking.