1. Put the Soya sauce, onion, ginger, garlic,vinegar, sugar, tomato puree, salt and pepper in a saucepan.
2. Bring to a boil and simmer for 2 minutes.
3. Soak the dried mushrooms in warm water for half an hour. Then drain, rinse and cut into thin slices.
4. Heat the oil in a saucepan and add the chicken shreds. Cook for 3-4 minutes.
5. Add the stock and the Soya sauce mixture, together with the cornflour mixed with sherry, to the chicken.
6. Add the mushrooms and cook till sauce thickens slightly.
7. Serve hot.