Mix the tofu with soy sauce, briefly marinate. Heat the oil in a wok or a wide-bottomed frying pan, reduce the heat. Pat the tofu dry, stir-fry in batches for approx. 3 mins., remove, cover and keep warm. In the same pan, bring the water to the boil with all the ingredients up to and including sugar, reduce the heat, simmer for approx. 3 mins. Add the onions and courgettes, reduce the heat and simmer for approx. 10 mins. until almost soft. Add the peppers, simmer for about another 5 mins. Stir in the tofu and chilli, gently heat, season and serve with coriander.