Keep it aside for 10 to 20 minutes. Cook the marinated chicken in medium thick coconutmilk, till the chicken becomes tender(pressure cooker is not recommended).
Add remaining coriander powder & garam masala. Fry it till the oil starts appearing. Add the sliced tomatoes. When tomato becomes soft add cooked chicken along with the gravy. Combine well.
Add thick coconutmilk and cook for 5-7 minutes. Chicken mappas is ready.