Wash the fish steaks; slice the onions into rings, finely mince the chillis, ginger and garlic. Heat a little oil and fry the onions until golden. Add the chillis, ginger and garlic and fry for five minutes.
Add the vinegar and remaining ingredients and simmer gently for five minutes. Add the fish and, if necessary, 1-2 tablespoons of water. Simmer until fish is cooked and the gravy is thick. Garnish with coriander leaves and serve with rice or bread.