For the marinade:

1/2 cup soy sauce
1/2 cup plum sauce
1/2 cup pineapple juice
1/2 cup ketchup
1/4 cup scallions, finely sliced
3 tablespoons cilantro, chopped
2 tablespoons fresh ginger, minced
2 tablespoons fresh garlic, minced
2 flank steaks, about 1-1/4 pounds each and 3/4 inch thick

To make the marinade: In a medium bowl, combine the marinade ingredients.

Trim the flank steaks of any surface fat and then place in a large, resealable plastic bag. Pour in the marinade, press the air out of the bag, and seal tightly. Refrigerate for 3 to 6 hours, turning occasionally.

Remove the steaks from the bag and reserve the marinade. Pour the marinade into a small saucepan, bring to a boil, and boil for 1 full minute. Pat the steaks dry with paper towels and allow the steaks to stand at room temperature for 20 to 30 minutes before grilling. Grill over Direct High heat until cooked to desired doneness, 8 to 10 minutes for medium-rare, turning once. Remove from the grill and let rest for 3 to 5 minutes. Cut across the grain into thin strips. Serve warm with the sauce.