First cut the onions into ring shape and then separate the rings. Use the bigger rings first.
Now make the batter. For that mix all the ingredients except bread crumps. Add more soda water if required. Make a thick paste.
Now coat the onion rings with the batter then coat with the bread crumps. Prepare rest of the onion rings like this. Now keep this rings in freeze for 10 to 15 minutes.
In between heat the oil for frying.
After 15 minutes fry the rings in medium heat till golden brown and crispy.
serve.