I think albacore tuna loin is best cooked rare with a thin seared outer layer, but loins are usually thicker in the middle with tapered ends, so there will be more-done and less-done portions that will suit individual preferences. The marinade gives a classic Japanese flavor to the fish. If you’re in a hurry, even 30 minutes of marinating will do the job. Tuna cooked this way doesn’t need any condiment, but if you wish, you can serve it with wasabi paste and pickled ginger (both available from Japanese food stores and online).
Fast Food, Good Food More Than 150 Quick and Easy Ways to Put Healthy, Delicious Foods on the Table courtesy Little, Brown and Company Copyright © 2015 by Andrew Weil, MD
Mix the marinade ingredients until the sugar dissolves. Pour half the marinade over the tuna in a shallow dish, then cover. Place the tuna in the refrigerator for at least 30 minutes, turning occasionally to make sure all of it is flavored with the marinade.
Remove the tuna from the refrigerator 20 minutes before cooking.
In a small saucepan, bring the remaining marinade and 2 tablespoons of water to a gentle boil and allow it to reduce a little. Reserve.
Heat the grapeseed oil in a nonstick skillet over high heat until hot but not smoking.
Place the tuna in the hot oil and sear on each side to desired doneness. For rare, this may be just 2 minutes on each side. (Check the ends or slice through the middle to check doneness.)
Remove the tuna loin to a heated platter and cut into 1/2- to 1-inch slices, as desired. Drizzle the sauce over the tuna and serve immediately.