Pre heat the oven to 180 degrees Celsius.
Wipe the mackerel with a damp cloth and drizzle a little olive oil over each fillet. Season with black pepper and sea salt and set aside.
Combine the cucumber, capers, chilli, onion, coriander and lime juice together and set aside to allow the flavours to combine.
Wash the potatoes place them in pan of salted water to boil for 15 to 20 minutes.
Heat an oiled BBQ or grill pan to hot and add the mackerel to sear for a couple of minutes. Turn the fish and sear on the other side.
Place the mackerel on a baking tray in the oven for a further 10 to 12 minutes to cook through.
Steam the bok choy in the last 4 minutes and serve the fish with the salsa on the side with accompanying new potatoes and bok choy.