Step 1Season steaks with salt and pepper, and let stand 10 minutes at room temperature.
Step 2Combine soy sauce, sesame oil, Worcestershire sauce, garlic, and brown onion in blender and puree until smooth. Pour over steaks and marinate 5 to 10 minutes.
Step 3Remove steaks from marinade. Cook steaks on grill pan over high heat until desired doneness, about 3 to 5 minutes per side for rare. (Steaks can also be cooked on outdoor grill.) While preparing steaks, grill red onion a few minutes on each side. Remove steaks from grill pan, sprinkle with toasted sesame seeds and let rest 5 minutes. Serve with grilled onion.