Lay the tuna steaks in one layer in a shallow baking dish and pour two thirds of the vinaigrette over them. Turn the tuna to coat well. Cover with cling film and place in the fridge for 15 minutes.
For the griddled lemon and parsley tuna, place the tuna steaks in a medium bowl with the olive oil, lemon zest and juice and parsley. Heat a griddle pan, add the tuna steaks and fry on each side ...
Set aside to cool. Slice the tuna into 11/2-inch cubes and cut each cube into 1/8-inch-thick squares. Mix the cream cheese with the wasabi until smooth, and season to taste with lime juice and salt.