Combine sesame seeds, wasabi powder, soy sauce, honey and sesame oil in a shallow pan. Add steak, turning to coat both sides. Let marinate for 10 minutes, then turn and marinate for 10 minutes more.
Heat peanut oil in a heavy nonstick skillet over medium-high heat. Cook steak to desired doneness, about 2 minutes per side for a nice sear on the outside and a rare middle or 3 minutes for medium-rare.
Top with a sprinkle of green onions, if desired, and a squeeze of lime.