In a medium mixing bowl, combine the soy sauce, sesame oil, olive oil, lime juice, garlic powder, ground ginger, and black pepper. Whisk until well blended.
Place the ahi tuna steaks in the marinade and coat them evenly. Let the tuna marinate for about 10 minutes. This allows the flavors to penetrate the fish without overpowering its natural taste.
Heat a large skillet or cast iron pan over high heat. Add a drizzle of olive oil and let the pan get very hot. This is important for creating a nice sear on the outside of the tuna steaks.
Once the pan is hot, carefully place the tuna steaks into the pan using tongs. Sear the tuna for about 1–2 minutes on each side.
You want a crispy, browned crust on the outside while keeping the inside rare. If you prefer your tuna more cooked, you can add an additional minute on each side.
Remove the tuna from the pan and let it rest for 2 minutes on a cutting board. Use a sharp knife to slice the tuna into thin pieces.
Sprinkle sesame seeds over the tuna for added texture and garnish with fresh cilantro if desired. Serve with your favorite side dishes like steamed vegetables or rice.