From BBC website (but basically the same as I would do)
Ingredients 2 tbsp vegetable oil 4 skinless, boneless chicken breasts, cut into 2.5cm/1in cubes 1 small red pepper, de-seeded and cut into 2.5cm/1in pieces 1 small green pepper, de-seeded and cut into 2.5cm/1in pieces thick thumb-size piece of fresh ginger, peeled and finely chopped 6 garlic cloves, chopped 1x220g can water chestnuts, drained and sliced 1 bunch spring onions, cut into 2.5cm/1in pieces 1 small can sliced pineapple, drained and cut into chunks (optional) ground white pepper For the sauce: 1 tbsp soft light brown sugar 2 tbsp rice vinegar 3 tbsp rice wine or dry sherry 2 tbsp dark soy sauce 175 ml/6fl oz chicken stock 2 tbsp tomato purée 2 tbsp cornflour mixed with 2 tbsp water
Method 1. Heat the oil in a wok or large frying pan. Add the chicken, peppers, ginger and garlic. Fry for 2-3 minutes, then add the water chestnuts, spring onions and pineapple, if using, and fry for about 30 seconds. 2. Add all the sauce ingredients and bring to the boil. Reduce the heat and simmer for about 6 minutes. Season with white pepper.