How to Make It
In a large nonstick frying pan, heat 1 tablespoon of the oil over moderately high heat. Sprinkle 1/4 teaspoon each of the salt and the pepper over the tuna. Cook the fish for 2 minutes. Turn and cook until done to your taste, 2 to 3 minutes longer for medium rare. Transfer the tuna to a carving board.
In a small glass or stainless-steel bowl, whisk together the lemon juice, garlic, and the remaining 1/4 teaspoon salt and 1/2 teaspoon pepper. Add the remaining 6 tablespoons oil slowly, whisking.
Cut the tuna into 1/2-inch-thick slices. In a large glass or stainless-steel bowl, combine the lettuce and the radishes and toss with all but 2 tablespoons of the vinaigrette.
Put the salad on plates. Top with the tuna slices and drizzle the remaining vinaigrette over the top.
Variation: Substitute two six-ounce cans of drained canned tuna for the fresh tuna. Skip Step 1 completely and add the drained canned tuna along with the lettuce and radishes.
Wine Recommendation: Pinot noir works beautifully with meaty fish such as salmon, swordfish, and especially tuna. For this salad, pour one of the many excellent examples from Oregon, where pinot noirs have bright raspberry flavors and a refreshing, lively crispness.
Quick From Scratch Soups & Salads