Step #1 In a mixer process the onion, garlic, & ginger, add little water to make a smooth paste.
Step #2 Heat the oil in a pan over med-heat/flame & fry the onion/garlic mix for 5 mins.
Step #3 Add the turmeric,and the chilli powder, turn heat to low & cook for 30 mins, cumin, ground coriander, stirring often so that the mix does not stick or burn.
Step #4 Add half of the tomatoes & cook for 2 mins.
Step #5 Add the chicken stir & cook till the meat changes colour, 5 mins Now add the rest of the tomatoes & any juice.
Step #6 Add the salt & water, bring to the b oil, reduce the heat & let simmer covered till the chicken is tender.
Step #7 stir this to prevent sticking.
Step #8 Add the green chillies & garam masala, cover & cook for 5 mins.