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)
1. Combine all marinade ingredients. Mix well.
2. Place flank steak in a resealable plastic bag and add marinade. Refrigerate for 3 to 6 hours, turning occasionally to distribute marinade.
3. Remove flank steak from the marinade. Reserve marinade. Place steak in center of cooking grate and grill for 15 to 20 minutes, or until desired doneness, turning once halfway through grilling time. Occasionally brush lightly with remaining marinade while grilling. Remove steak when done and hold in a warm place for 5 to 7 minutes. Slice thinly on the bias for serving.
4. Meanwhile, bring remaining marinade to a boil and simmer rapidly for 5 minutes. Serve with steak.