Bring about 5 cups water to a boil in large saucepan. Add green beans; cook 3 minutes. Add carrots and cauliflower. Return to a boil; boil 2 to 3 minutes or just until blanched. Drain; rinse with cold water to cool.
In small bowl, combine salad dressing, dill and salt; blend well.
In large nonmetal bowl, combine blanched vegetables, mushrooms and bell peppers. Add dressing mixture; toss to coat. Cover; refrigerate at least 30 minutes or until serving time.
To serve, line platter with lettuce leaves. Arrange vegetables over lettuce.