Allow the Ahi Tuna steaks to thaw slowly in the refrigerator overnight for the best texture and flavor retention.
In a mixing bowl, combine soy sauce, honey, half of the cooking oil, salt, and black pepper. Whisk until the mixture is smooth and well-blended. Place the tuna steaks in the marinade, turning to coat all sides evenly. Let the fish marinate for at least 30 minutes in the refrigerator, or for a quicker option, 5 to 10 minutes at room temperature.
Spread the sesame seeds on a flat plate. Once marinated, press both sides of the tuna steaks into the sesame seeds, ensuring a generous and even coating.
Heat the remaining oil in a heavy-bottomed skillet over high heat until shimmering. Carefully place the sesame-coated tuna into the pan. Sear each side for 2 to 3 minutes—just enough to form a golden crust while keeping the center beautifully rare.
Transfer the tuna to a cutting board and slice into thick, even pieces. Finish with a scatter of fresh spring onion for a vibrant, aromatic garnish. Serve immediately for the best experience.