Whisk the egg mix ingredients together in a bowl. Roughly chop the spring onion and cut the tomato into eighths. Mix the sauce ingredients together in a small bowl or ramekin.
Now build your wok clock (a term the School of Wok uses for how to manage your ingredients by setting them up in order of cooking around a circular plate): place the tomatoes at 12 o’clock, then the egg mix, followed by the spring onion and lastly the sauce.
Bring the vegetable oil to a smoking hot heat in a wok, then add the tomatoes and fold through the oil, so that the skin blisters slightly. Remove the tomatoes with a slotted spoon and put back on the top of the spring onions on the wok clock. Now pour half the hot oil from the wok into a small ceramic or metal bowl, so that the finished egg does not come out too greasy.
Heat the wok up once more to a smoking hot temperature. Slowly pour the egg mix into the wok and swirl gently around, keep the wok on a high heat. start to fold the egg into itself with a spatula or wok ladle, while continuing to swirl the wok around at the same time. Once the egg is just over half way cooked and starting to become firmer on the edges but still wobbly, add the tomatoes back in, along with the spring onions. Pour the sauce into the wok, maintaining a high heat for 30 seconds. Toss the wok once or twice, to mix the ingredients and finish cooking the egg, then take off the heat and serve- a truly classic Hong Kong dish. Accompany with a side of dolly noodles or some good thick toast or crusty roll with butter.