FOR each portion (2 servings): Heat wok or saute pan on medium heat. Add oil, ginger and garlic; saute briefly. Add mussels; pan roast 1 min. Stir in sake, steak sauce, vinegar, soybean paste and pepper; cover. Cook until mussels are fully opened.
DISCARD any unopened mussels. Pour remaining mussels into heated bowl. Garnish with 1/4 cup couscous and 2 Tbsp. scallions.