Scrub the potatoes clean and place in a saucepan of cold water, bring to the boil and let it cook until the potatoes are soft. Drain and dry.
Season the hake, you can remove the skin if you so desire. Place the fillet in a steamer and cover with a lid. If steaming in a saucepan, fill the pan with a layer of water and place the steamer on top, making sure that it does not come into contact with the water. Heat the water to a gentle simmer before adding the fillets of hake.
Cook for 8-10 minutes until the hake is cooked through - the cooking time will vary depending on the thickness of the fillet. Finish off with a squeeze of lemon juice or lime juice. Set aside.
When plating, score the surface of each potato half with a sharp knife in a criss-cross pattern. Add the mayonnaise. Add the fish and served with a salad.