In small nonmetal bowl, combine all dressing ingredients; mix well. Refrigerate.
Cook lima beans as directed on package. Drain. Cook orzo to desired doneness as directed on package. Drain. In colander or strainer, rinse lima beans and orzo with cold water to cool. Drain well.
In large bowl, combine cooked lima beans and orzo, bell pepper, celery, raisins and onion; toss gently. Pour dressing over mixture; toss to coat. Refrigerate at least 2 hours to blend flavors.
Just before serving, add tomatoes; toss gently. To serve, line plates with lettuce. Spoon salad onto lettuce. If desired, garnish with additional fresh cilantro.