One great recipe for a simple seared tuna steaks is Seared Tuna Pepper Steaks from Epicurious. Sesame oil, soy sauce, sherry and coarse black pepper add a tangy Asian flavor to this dish.
Start with four 6 to 7-ounce tuna steaks that are around 1 inch thick. Sprinkle both sides of the steaks with salt and some coarse ground pepper. Press these spices gently into the tuna flesh. Heat 2 teaspoons of sesame oil over high heat in a large non-stick skillet. Add tuna steaks, and sear until the outsides are brown and the middle is opaque, and this should take about three minutes per side. Use tongs to remove the steaks to a platter, then tent them with foil to retain heat.
Add 1/4 cup of dry sherry and 2 tablespoons of soy sauce to the skillet. Turn the heat down, and simmer until slightly reduced, about one minute. Scrape any brown bits from sides of pan, pour the sauce over the tuna steaks to serve, and top it with 2 tablespoons of chopped green onion tops or chives. This dish goes well with mashed potatoes, roasted potatoes and rice. Most of the people who reviewed this recipe said they would make it again.