Combine first 7 ingredients in a blender; process 1 minute or until onions are finely chopped. Transfer sake mixture to a large zip-top plastic bag. Add steak to bag; seal. Marinate in refrigerator at least 2 and up to 8 hours, turning occasionally.
Remove steak from bag, reserving marinade. Pat steak dry with paper towels. Heat a large nonstick skillet over medium-high heat. Lightly spray both sides of steak with cooking spray. Add steak to pan; cook 1 minute on each side or until browned. Remove steak from pan; keep warm. Add reserved marinade to pan, and cook 4 minutes or until thick and deep brown in color, stirring constantly. Return steak to pan, turning to coat. Cook 2 minutes or until desired degree of doneness. Let steak stand 5 minutes. Cut steak diagonally across grain into thin slices.