In a pan, heat oil and add the garam masala and onions. Saute the onions for a while. Then, add the ginger garlic paste and saute. Then, add the tomatoes, turmeric powder, chilli powder, coriander powder, cumin seed powder, green chillies and salt. Fry this mixture for a while maybe adding a little bit of water. Then, add the chicken pieces and some water and cover the pan with a lid and allow to cook for 1/2-1hr. Once the oil starts to come out to the top, stir in the coconut milk and bring to a boil. Add the curry leaves and coriander leaves for garnish. Serve hot Goes well with rice and rotis.