For our purposes, the slightly pungent flavor of wasabi mashed potatoes cuts through the creamy potatoes' richness, as well as elevates the tuna steak's umami taste. Here's one for the fruit lovers.
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.