Mix Besan, cumin seeds, carom seeds, turmeric powder, chopped green chilli, coriander leaves, chopped onion and salt in a large bowl.
Add water to make pourable and thick batter (like dosa batter).
Heat a nonstick pan on medium flame, apply oil to pan surface and pour a ladleful batter on it. Spread it in a round shape.
Once one side is cooked, turn the chilla and apply little amount of oil.
Cook until golden brown from both side.
Served hot with green chutney or tomato sauce.