Grind the coriander seeds in a spice grinder and set aside. After the chicken is finished marinating, heat up a little less than 1/4 cup vegetable oil in a pot. When oil is hot, add cumin seeds and let them cook for 15 to 20 seconds until you smell them and they turn a little darker in color. Add chopped onion, 1/2 tsp salt and sauté until soft. Add ginger, garlic, green chiles and sauté until golden brown. Add ground turmeric, chili powder, coriander powder and garam masala. Stir for about 15 seconds until the raw smell of the spices go away. Turn heat down first to preventing burning of spices.