Score both sides of meat with knife in diamond pattern at 1-inch intervals.
Whisk oil, soy sauce, lemon juice, garlic, pepper flakes, salt and pepper. Pour into plastic food-storage bag. Add steak; marinate in refrigerator for 4 hours or overnight.
To cook, prepare outdoor grill with hot coals, or heat gas grill to hot (to broil, see below). Remove steak from marinade; discard marinade.
Grill about 2 minutes per side or until grill marks appear. Move to cooler part of grill; cook covered, 12 minutes or until instant-read meat thermometer inserted in center of meat registers 145 degrees F. Let meat rest 10 minutes before slicing.
Process vinegar, soy sauce, scallion, ginger and pepper in food processor until smooth. With machine running, gradually add oil through feed tube. Process until thick and smooth.
Toss lettuce with dressing in bowl. To serve, arrange sliced steak over lettuce on platter. Makes 6 servings.