Put all the ingredients under "crush to form a paste" in a mortar and pestle and grind to form as fine a paste as possible.
Cut the fish fillets into two and make small slits in them. Smear the paste equally over all the fillets and marinate in the refrigerator for 20-30 mins.
Pre heat oven to 375F
Line the fish on a baking tray with parchment paper on it and bake for 20 mins. To finish it off, broil on high for 3-4 mins.
Serve with raw red onion slices and lime wedges.
Notes
To check for doneness: teh spice / masala paste on the fish should have changed color slightly and not look too raw.