Remove all visible fat from pork. Partially freeze meat; slice thinly into strips. Stir together in a bowl of soy sauce and cornflour. Add stock and set aside.

Heat oil in wok or non-stick pan over high heat. Add garlic and ginger root and cook for 1/2 minute. Add celery and shallots and cook lightly. The vegetables should be slightly crisp, not overcooked. Remove vegetables and keep warm.

Add pork to the hot wok or pan and dry fry until brown. Stir continuously. Add stock mixture to pork, cook and stir until thick and bubbly. Add cooked vegetables and tomatoes. Cover and cook for 1 minute. Serve at once.