Pat the ahi tuna steaks dry with a paper towel. Place on a plate or inside a plastic bag.
Mix the soy sauce (2 tablespoons), toasted sesame oil (1 tablespoon), honey (1 tablespoon) kosher salt (1/2 teaspoon- OMIT if marinating for more than a couple hours, see notes), pepper (1/4 teaspoon), and cayenne pepper (1/4 teaspoon) 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 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 canola oil (1 tablespoon) to the hot pan. Sear the tuna for 2 minutes on each side for medium-rare (1.5 minutes on each side for rare; 3 on each side for medium). (Note: different burners get hotter depending on your stove. Use your best judgment whether you use medium, medium-high, or high heat, as the marinade may burn if too high heat is used)
Remove to a cutting board and allow to rest for at least 3 minutes. Slice into 1/2 inch slices and serve garnished with green onions, toasted sesame seeds, and a squeeze of fresh lime juice, if desired.