Preheat oven to 450 degrees F. Finely shred 2 teaspoons peel from one lemon. Squeeze juice from lemon. For dressing, in small bowl whisk together oil, lemon peel and juice, pepper, and salt; set aside. Cut remaining lemon in wedges; set aside.
Place asparagus in single layer in shallow baking pan. Drizzle 2 tablespoons dressing. Bake, uncovered, for 8 minutes.
Meanwhile, heat 1 tablespoon dressing in large skillet. Add tuna; cook 4 to 6 minutes each side, until browned and center is slightly pink.
Divide greens among 4 plates; top with tuna and asparagus. Drizzle remaining dressing. Sprinkle Parmesan; pass lemon wedges. Makes 4 servings.