For the tuna, place the tuna on a plate, season, to taste, with sea salt and freshly ground black pepper. Sprinkle over half ofthe sesame seeds onto one side of the tuna, patting them onto the tuna steak, then repeat on the other side.
Heat the oil in a griddle pan until smoking. Add the tuna and cook over a high heat for two minutes on each side, or until cooked to your taste.
For the salsa, place all the ingredients in a bowl and stir to combine.
To serve, remove the tuna from the pan and place onto a serving plate. Spoon the salsa on the plate and garnish with the parsley.