Sprinkle half the salt on the tray. Put the cod fillet on it, sprinkle with the remaining salt and refrigerate for 1 hour.
Peel and chop shallots, garlic and hot peppers. Heat the coriander and cumin seeds in a dry frying pan until fragrant. Add the turmeric and peanuts and cook over moderate heat for a couple more minutes.
Place the onion, garlic, pepper, peanuts and spices in a blender and chop. Add coconut milk, sugar and fish sauce, blend again until a smooth paste forms. Add some water if necessary.
Remove the fish from the salt and rinse under running water. Dry with napkins, place on a dish and carefully cover with spice paste. Leave for 1 hour at room temperature.
Ignite the coals, set the grate over the flame and heat it up properly. Grease the grate with vegetable oil.
Remove fish from marinade, shake off excess. Place on a wire rack and grill for 3-5 minutes on each side.