First, heat up oil in a pan. Add cumin seeds and cook until you smell them, about 30 seconds. Add chopped onion, pinch of salt and sauté until soft. Add chopped ginger, garlic and green chiles. Sauté until golden. Add coriander, turmeric and chili powder. Stir for 30 seconds until raw flavor goes away. Lower heat to prevent spices from burning. Add chopped tomatoes, ½ tsp coarse salt and stir. Cover and cook until soft and oil has separated. Stir once in a while.