Heat the oil in a wok or large frying pan, add the onion and fry until soft.
Mix the turmeric, coriander, cumin and chilli powder in a bowl with the water. Stir in to the onion and simmer until the liquid has dried up – about 3-4 minutes. Add the chicken and fry on all sides, then add the tomatoes and a pinch of salt. Cover and cook for 15 minutes.
Add the green pepper, garlic and chillies. Cook, uncovered, until all the tomato juices have evaporated and the chicken is cooked. Eat with naan bread and rice and salad.