Mackerel with apple purée

2) Push the mixture through a sieve to make a purée. Set aside to cool.
3) To cook the mackerel, score the skin on each piece. Sprinkle salt on the skin only and place skin-side up under a hot grill for 5-6 minutes.
4) To serve, mix the salad leaves with the watercress, divide over 4 plates, drizzle with the oil. Add the mackerel and apple purée.