Place couscous in large bowl. Pour 1 cup boiling water over couscous and let stand. In saucepan, bring vegetable stock to boil, add thyme and vinegar. Boil to reduce to 3/4 cups. Add peas and corn to liquid and turn off heat. Toss tomatoes, scallions, and basil into couscous. Add liquid to couscous and mix well.
Cover and refrigerate 2 hours before serving. To serve, top a romaine leaf with couscous mixture. Makes 6 servings
Per serving:197 calories, 2 grams fat