In a small bowl mix together the marinade ingredients: the soy sauce, oil, brown sugar, sesame seeds, scallions, and garlic. Marinate the steaks for one hour, covered, in the refrigerator.
While the steak is marinating, toss together the arugula, pears, and radishes in a large bowl. Combine the rest of the ingredients in a small jar. Dress the salad right before serving.
When the steak is done marinating, heat a cast iron skillet on high heat.
Cook the steaks, for about 5 minutes per side, until it reaches 145 degrees for medium rare. If you like your steaks more well done, you may want to sear both sides, and then put the skillet in a 350 degree oven for about 10 minutes.
Let the steak sit for about five minutes on a cutting board, and then cut it into thin slices. Sprinkle it with extra sesame seeds and serve it with the salad.