In a saucepan combine everything except capers and dressing. Bring to a boil, reduce heat and simmer mixture, covered, for 18 minutes or until lentils are just tender. Drain, discard bay leaf, and chill, covered, in a metal bowl for 10 minutes. Whisk capers with dressing, toss dressing with lentils, serve on lettuce leaves.
To make dressing, in a bowl combine vinegar, mustard, salt and pepper to taste, add oil in stream, whisking until emulsified. Stir in herbs. Makes 2/3 cup.