Step by step

Add the tuna to the potatoes and mix well

If you are a real gourmet connoisseur of fish and you can afford it, as opposed Yellowfin tuna you could buy Bluefin tuna, the most prized variety for the quality of its meat, although it is now an endangered species.
Tuna - of which there are many different species - can be bought as bottarga (tuna eggs), or the ‘mosciame’ or ‘ventresca’, the most prized part of the fish.