Heat a little olive oil in a large frying pan. Season the fish and add to the pan, skin side up. Fry for 3-4 minutes then turn it over. Add a knob of butter to the pan and continue to cook the fish for another 3-4 minutes until it flakes easily with a fork. As the butter melts spoon it over the fish.
Meanwhile combine the salad ingredients. Taste for seasoning.
Heat the milk and butter in a saucepan then combine with the cooked potatoes and peas. Mash well. Season to taste.