Ahi Tuna Steak Sandwich

¼ teaspoon prepared wasabi or 2 teaspoons prepared horseradish, or to taste
2 tablespoons low-fat mayonnaise (no more than 2 g fat per tablespoon; I used Best Foods/Hellmann’s)
½ teaspoon extra virgin olive oil2 (4-ounce) sashimi- or sushi-grade ahi tuna fillets
Sea salt and freshly ground black pepper, to taste
2 (about 3 ½-inch-diameter) whole-wheat or whole-grain hamburger buns
6 thin plum tomato slices, or 2 to 4 larger slices
1 small leaf green lettuce, cut in half, or more to taste

It’s important, when making this sandwich, that you have all of your ingredients prepped and ready to go before cooking the tuna.

Stir the wasabi or horseradish into the mayonnaise until well combined. Add more to taste, if desired. Set aside.
If the fillets are thicker than ¾ inch or are not at least slightly larger than the buns, place them between 2 sheets of waxed paper or plastic wrap. Using the flat side of a meat mallet or the bottom of a skillet, pound them until they are slightly larger than the buns.
Rub the olive oil evenly over the entire fillets. Season both sides of the fillets with salt and pepper.
Place a small nonstick skillet over high heat. When very hot (but not so hot that the pan smokes), add the fillets. Sear them so the outsides are golden brown in spots but the insides are rare, 30 seconds to 1 minute per side.
Meanwhile, place half a lettuce leaf and 3 tomato slices on each bun bottom. Top each with 1 fillet. Spoon half of the reserved mayonnaise mixture on each bun top and flip them atop the sandwiches. Serve immediately.