Trim the tuna loin of any tendon and bloodline and pull the loin as smooth and straight as possible. Place the loin in the freezer, for approx half an hour.
Sharpen your knife.
Put a few tablespoons of pesto into a mixing bowl and add enough olive oil to give it a runny consistency yet very green. Cut the caper berries in half from the stem down.
Arrange the 4 serving plates on your workbench, near your chopping board.
Remove the loin from the freezer and with your very sharp knife start slicing across the grain and place the very thin slices on the plates in 1 layer.v Toss the arugula with a little lemon juice, olive oil and salt and pepper and set aside.
Place a few caper berries randomly on each plate, drizzle a pattern of pesto oil onto the fish.
Squeeze a little lemon juice over the fish and season with pepper and a small pinch of salt.
Place a small handful of lettuce on the centre of each plate and voila, you’re done, so go sit down with your guests and enjoy with a nice medium bodied white. Verdehlo and pinot grigio pair nicely with this dish.