Blend tamari sauce with 1 tablespoon oil. Place tuna steaks in soy mixture to coat; set aside to marinade.
In a small bowl, combine sesame seeds and seasonings; press evenly over both sides of tuna steaks.
Heat 1 tablespoon oil in a 12-inch non-stick skillet over medium heat. Cook tuna 2 to 3 minutes per side. Use care not to overcook tuna; it is best eaten rare. The center should still have a pink color. Remove steaks from heat and let sit for 2-3 minutes before slicing into thin slices.
In a small bowl, combine ingredients for Wasabi Vinaigrette; set aside.
Arrange ingredients for salad on 4 serving plates. Top with tuna slices and drizzle with vinaigrette just before serving.