Whisk together the soy sauce, sesame oil, garlic, honey, ginger, cayenne, salt, and pepper in bowl. Set aside 2 tablespoons of the mixture in a cup.
Put the tuna steaks in a plastic zip loc bag and pour the marinade over them. Push the air out of the bag and seal. Gently work the marinade around the tuna steaks ensuring they are covered.
Let the tuna marinate in the refrigerator for about 10 minutes.
Heat a non-stick skillet over medium-high to high heat. Add 1 tablespoon olive oil or other oil to the pan.
Place the marinated ahi tuna steaks in the pan. Sear for 2 minutes on each side (medium rare). For rarer, reduce the time to 1 ½ minutes on each side. For medium, increase the time to 3 minutes on each side.
Immediately remove the tuna steaks from the pan and place on plate. Let them rest for 3 minutes.
To serve, slice the tuna steaks and garnish with the marinade you set aside. Add chopped green onions. Drizzle with fresh lime juice if desired.