Wash the fish thoroughly with water, then pat dry. Rub the fish with a mixture of lemon juice, pinch of salt and a pinch of coriander. Let the fish stand for 30 minutes, and drain off the released water.
Make the marinade for the fish, by mixing yoghurt, ground ginger, garlic powder and garam masala together.
Marinate the fish in the yoghurt for 1 hour (the longer left to infuse the better).
Grill the fish on a charcoal barbecue for 5 to 7 minutes (each side), or place under the oven's grill for the same amount of time. You can also bake the fish for 15 to 20 min at 200 C / Gas 6; keep turning the on each side while baking every few minutes. Add a side salad, or roasted vegetables if eating this as a main.
For a similar dish, look up Tandoori fish, with is a slight variation but marinated and cooked in ghee or butter.