Step 1

In a mixing bowl, whisk the first 8 ingredients (everything but oil and tuna steaks) for the marinade.

Step 2

Place the tuna steaks on a rimmed pan or casserole dish, and pour marinade over the fish.

Step 3

Marinate for 15 minutes, turning once halfway through the marinating process. Pour off the marinade from the fish.

Step 4

Heat a few tablespoons of oil in a cast-iron skillet over medium-high heat, until shimmering.

Step 5

Carefully place tuna steaks in the skillet with plenty of room between them. *

Step 6

Sear 3 minutes per side. Carefully flip with tongs or a spatula.

Step 7

Transfer fish to a large cutting board or plate, cover with foil, and allow to rest for 10 minutes.

Step 8

Using a sharp knife (serrated is best), slice thinly across the grain (perpendicular to the natural lines across the fish).

Step 9

Garnish with green onion and sesame seeds if desired. Serve chilled or at room temperature.