Mix soy sauce, oil, 3 teaspoons ginger (or more), and garlic in resealabel plastic bag. Add flank steak and seal bag; turn to coat. Let stand at room temperature for 30 minutes, turning occasionally. Or, preferably, you can refigerate for several days. You can even freeze it. The ginger tenderizes the steak. I can't speak to the chemistry here, but I have found that marinating up to six days makes the fairly tough flank steak about as tender as tenderloin.

Stir sugar and vinegar in small saucepan over medium heat until sugar dissolves; remove from heat. Add jalapenos and remaining 2 teaspoons ginder. Shred cabbage like cole slaw and place in bowl with 1.2 cup green onions. Pour vinegar mixture over and toss to coat. Season with salt and pepper. Let stnade while grilling steak, tossing occasionally.

Grill steak until cooked to desired doneness, about 6 minutes per side for medium-rare. Trnasfer to work surface. Let rest for 5 minutes. Slice steak thinly against grain. Sprinkle 1/4 cup green onions over slaw.