Soak the dal overnight. Grind it with the green chillies, ginger, garlic, salt and turmeric adding little water from time to time. The paste should not get watery rather it should be of the consistency that you can shape them into vadas.
Add the chopped cilantro to this coarse paste and also the onions, if you are using the onions.
Shape the paste into small flat vadas and Deep Fried them. Drain them on paper towels. Serve hot.