Heat the oil. Finely slice all the vegetables and cook until tender and then add the spices. Drain the ackee and add to the cooked vegetables, stirring very gently so as not to break the ackee. Cook for 3-5 minutes so that the ackee is heated through. Add the chopped tomato, freshly ground pepper and mackerel, then cook for a further 1 minute. Serve immediately.