Heat 1 tablespoon of the oil in a wok or frying pan, add the garlic, 2 spring onions and celery and cook for 1 minute. Increase the heat, add the chicken and pork and cook for 2 minutes.
Blend the cornflour with 1 tablespoon water. Stir into the sauce with the sherry and soy sauce and simmer, stirring occasionally, for 15 minutes.
Meanwhile, make the omelet.
Season the eggs with salt and pepper to taste. Heat the remaining 2 tablespoons oil in a large frying pan pour in the eggs and cook gently, drawing the cooked edges towards the centre with a fork, until set and browned on both sides.
Carefully transfer to a warmed serving dish. Spoon over the meat sauce and garnish with spring onions and celery leaves. Serve immediately.