It is imperative that the fish be absolutely fresh as it should be cooked with the head on and not gutted. If you can not bring yourself to cook the fish un-gutted then make sure the cavity is firmly sealed with toothpicks before cooking.
Per portion you will require:
Spread half the salt in an oven dish and lay the fish on top. Cover the fish completely with the remaining salt. This can be made easier by slightly moistening the salt.
Bake it in a preheated oven at about 250oC (390-490oF), for 20-25 minutes.
Remove from the oven and break the salt crust open with a mallet and transfer the fish to a serving dish. Serve garnished with lemon and parsley.