To prepare sauce, in small bowl, combine first 5 ingredients; mix well. Set aside. Fill serving platter with crushed ice; arrange oyster shells over bed of ice. Place a half-slice lemon and a mushroom cap on each shell. Fill each mushroom with 1 oyster. Top each with an equal amount of sauce; sprinkle with parsley. Makes 4 servings. Each serving provides: 1 Pro Ex, 1-3/4 Veg Ex. Per serving: 56 cal, 5 g pro, 1 g fat, 8 g car, 71 mg sod.