Heat 2 tablespoons oil in a frying pan and sear all the chicken pieces lightly on both sides and transfer to a paper towel-lined platter
Roast cumin seeds, coriander seeds, and coconut lightly., and grind in a coffee grinder and remove to a bowl.
In a blender, add yogurt, onion, ginger/garlic paste, green chilies, ½ tablespoon cilantro, ground cumin, coriander, coconut mixture, chili powder, turmeric, tamarind or kokum pieces, tomato paste, salt, and water. Blend to a fine paste.
Heat ¼ cup oil in a heavy saucepan. Add the prepared spice sauce from the blender and cook covered on medium heat until spices get well fried. A deeper saucepan is highly recommended because of spluttering which might occur. Cook on slow heat until well fried.
Add enough water, or the amount for desired thickness of the gravy, about 1 ½ cup. Clean the sides well while putting the water. Bring back to a boil.
Add the seared chicken to the sauce, coat well by gently pouring sauce over the chicken. Bring to a boil, then lower heat and simmer for 30 to 35 minutes.
Transfer to a bowl and sprinkle remaining ½ tablespoon chopped cilantro for garnish to serve.
Serve with plain white rice.