In a medium bowl or glass measuring cup, whisk together the shoyu, lemon juice, sesame oil, garlic powder, sugar, salt and pepper to make a marinade. Pat dry the tuna steaks with paper towels and place in a glass or ceramic dish. Pour marinade over fish, turning to coat well throughout. Cover tightly and refrigerate for several hours; turn fish over at least once in the middle of the marinade time.

Heat 2 Tablespoons of oil in a large heavy skillet over medium high heat. Sear tuna steaks 1 ½ minutes per side, flipping carefully with a flat, steel spatula. If your steak is less than 1 ½ inches thick, sear for only 1 minute on each side.

Transfer seared steaks to a large cutting board and let rest for 5 minutes. Use a very sharp or serrated knife to slice thinly across the grain.

Serve warm or cold with optional garnishes or on top of a salad. Drizzle with Sriracha mayo if desired. This is delicious on a bed of greens mixed with cabbage and carrots or on a cold sesame noodle salad. I often eat this as a “bowl” meal with rice (black rice, sushi rice or cauliflower rice) + greens + roasted or grilled veggies + a sesame-tamari drizzle (1 teaspoon sesame oil + 1 Tablespoon tamari) or my Chinese chicken salad dressing from Quicker Than Quick.