1In small bowl, beat all vinaigrette ingredients with wire whisk until well blended. Cover; refrigerate.
2Lightly brush both sides of tuna fillets with oil; sprinkle with 1/2 teaspoon each salt and pepper. In 12-inch nonstick skillet, cook tuna over medium-high heat 1 minute on each side for rare doneness. Place on plate; refrigerate 5 to 10 minutes.
3On cutting board, cut tuna diagonally into 1/4-inch slices.
4On each of 4 plates, arrange 1 1/2 cups greens; top with 6 orange segments, 1 1/2 teaspoons onions and 1/2 teaspoon almonds. Arrange tuna on greens. Drizzle 3 tablespoons dressing over tuna and greens on each plate.