Pat the 2 ahi tuna (yellowfin tuna) steaks dry with a paper towel. Place on a plate or inside a plastic bag.
Mix the 2 tablespoons soy sauce, 1 tablespoon toasted sesame oil, 1 tablespoon honey, ½ teaspoon kosher salt (if using), ¼ teaspoon black pepper, and ¼ teaspoon cayenne pepper until honey is fully dissolved. Pour over the ahi tuna steaks and turn over to coat completely. Optional: allow to marinate for at least 10 minutes, or up to overnight in the refrigerator. Also optional: Reserve a spoonful or two of the marinade before coating the fish for drizzling on top after you've cooked it.
Heat a medium skillet (preferably non-stick or a well-seasoned cast iron skillet) on medium-high to high until very hot (or medium to medium-high for nonstick). I recommend giving cast iron 3-5 minutes to get hot and nonstick about 1 minute, depending on how thick it is.
Add the 1 tablespoon oil to the hot pan. Sear the tuna for 1 - 1½ minutes on each side for medium rare (2 -2½ minutes for medium-well to well, 30 seconds for very rare).
Remove to a cutting board. Slice into ½ inch slices and serve garnished with green onions, toasted sesame seeds, and lime wedges, if desired. If you find it needs more salt, I recommend sprinkling with flaky sea salt when serving.
