Pat the tuna steaks completely dry with paper towels. This is crucial for achieving a good sear.

In a small bowl, whisk together the sesame oil, soy sauce, grated ginger, minced garlic, honey (if using), and black pepper to create the marinade. Place the tuna steaks in a shallow dish and pour the marinade over them, ensuring they are coated. Let them marinate for at least 10 minutes at room temperature, or up to 30 minutes in the refrigerator.

Heat a cast iron skillet or heavy-bottomed frying pan over high heat until it's very hot – almost smoking. This high heat is key to getting a beautiful crust.

Carefully remove the tuna steaks from the marinade, letting any excess drip off. Place the steaks in the hot skillet. Sear for 1 to 2 minutes per side for rare (the center should be red and slightly warm), or 2 to 3 minutes per side for medium-rare (the center will be slightly pink). Avoid overcooking, as tuna can become tough and dry.

Once seared to your liking, immediately remove the tuna steaks from the skillet and place them on a clean cutting board. Let them rest for 2-3 minutes.

Slice the tuna steaks against the grain into 1/2-inch thick pieces. Garnish with sesame seeds and sliced green onions, if desired.