In a 3-quart saucepan bring water and salt to a boil and stir in couscous. Immediately remove pan from heat and let couscous stand, covered, 5 minutes.
Cut medium tomato into quarters and in a blender puree with mustard and vinegar until smooth. With motor running add oil in a slow stream. Season dressing with salt and pepper. Halve the cherry tomatoes and toss them with the couscous and torn basil leaves. Dress with the vinaigrette and serve.
Recipe courtesy of Gourmet Magazine