Rub the tuna steaks with sesame oil, and sprinkle with salt and pepper. Dip entire surface of each steak into sesame seeds. Place the tuna steaks in a very hot sauté pan and cook for only 1 minute on each side. Set aside.
Meanwhile, prepare vinaigrette. In a mixing bowl, whisk together all ingredients. Lightly coat salad with vinaigrette. Place on a platter.
Slice tuna steaks and place on top of salad. Drizzle remaining vinaigrette over the top.