I’m not sure where this whole “chicken of the sea” bit comes from. Tuna loin, the section of prime meat that lies next to the fish’s lateral line and provides most of the tail’s propulsive power, really benefits from being treated more like beef than fish – sear it quick and hot and serve it no more done than medium rare.
Marinate the steaks for at least an hour in your favorite teriyaki sauce (I like Soy Vay’s Island Teriyaki Sauce). Remove from the marinade and dust both sides with sesame seeds. I also like to hit it with a little Dizzy Pig’s Tsunami Spin or a good 5-Spice powder.
Now get your grill HOT!!! On the Big Green Egg this is easy – just open up all the vents and let it roar. On a charcoal grill you might want to consider getting a chimney starter full of coals hot and placing the cooking grate right on top of it. On a gasser, look for the “Nuclear” setting on your burner knob.
Grill the steaks for just 30 seconds to a minute per side. Rare tuna will be quite soft, with just a little resistance at the surface; medium-rare tuna will be gently yielding; and medium tuna will be firm. Anything past medium is cat food, so it’s best to pull the steaks off the heat just before they are done to your liking and let the carryover heat finish the job.
Slice the steaks thinly and serve drizzled with a little Teriyaki sauce or dark sesame oil.