1. Cut and scale the fish, then wash well.
2. Wipe dry, apply the ground paste all over, inside the stomach and head as well.
3. Make four ashes on either side of the fish with a sharp knife to allow the spices to permeate.
4. Let stand in a cool place for 1 hour.
5. Pierce the fish lengthwise with a skewer (seekh) (using two skewers if one is not long enough) and cook in a tandoor or on a charcoal barbecue.
6. If these methods of cooking are not available, cook under a grill or bake in the oven.
7. Turn the fish ever 10 minutes and cook till lightly browned.
8. Heat the oil and brush on the fish with a pastry brush, feather or piece of cotton wool while cooking.
9. When the fish is barely cooked, sprinkle with garam masala and cook till a dark golden brown.
10. Serve garnished with slices of lemon.