1. For the marinade, grind all the ingredients to a smooth paste.
2. Marinate the fish with this paste for at least 4-5 hours.
3. Wipe and oil the skewer before inserting it through the fish fillets.
4. Now roast the skewered fish in the tandoor, with the skewer standing upright (to allow drippings to fall off), for about 5 minutes.
5. Then baste with oil, cook for another 5 minutes or till done.
6. Remove the fish from the skewer, serve garnished with onion rings and lemon wedges, and sprinkled with chaat masala.