I love this fish dish. I happen to love Mackerel. I like Herring as well (which if I don't have Mackerel I can substitute.) The key to this dish (in my opinion is the combination of the spices and coconut milk).
2lb salted mackerel
1can of coconut milk (or make your own fresh)
1 cup water
A few sprigs of thyme (about 4 or 5)
3 garlic cloves
vinegar, black pepper and salt to taste (generally about 1 or 2 teaspoons of each)
1 tablespoon butter (I add this because it give the dish a nice flavor)
Soak mackerel in water overnight, changing water regularly. Boil the mackerel for 15 minutes then allow to cool. You can remove the mackerel heads if you want to. I leave mine on. Then cut the fish in to small pieces. Chop the onion, scallion, tomato and garlic. Combine the coconut milk and water in a saucepan, bring to the boil then turn the heat down to simmer. Add onion, scallion, tomato, garlic and thyme, cook for 10 minutes more.
If sauce is still watery, mix 1 tablespoon of flour in 1/4 cup of water and stir in to the mixture.
When finished you can serve it with traditional green banana and flour dumpling. Or you can use rice. A nice salad adds to the meal.