Mix the soy sauce, lime juice, sesame oil, pickled ginger and scallions together in a small bowl. Set aside.

Mix the wasabi powder and 2 teaspoons of water together in a small bowl to form a thick paste. Cover and set aside.

Preheat the grill with all burners set to high and the lid down till very hot, about 15 minutes.

Cut the tuna into 4 steaks, brush with the olive oil and sprinkle generously with the salt and pepper.

Grill the tuna covered turning once to the desired doneness, 5 to 6 minuted for rare, 7 to 8 for medium-rare

Cut the Tuna into 1/4 inch slices and fan out on individual plates. Drizzle a little soy sauce mixture over each plate, then place a dollop of wasabi paste on each plate, serve immediately