Avoid last-minute fuss by preparing the dressing and all the components up to 2 days in advance; toss together just before serving. Or save time with quick-cooking barley: In step 2, use 1 1/2 cups barley, 2 1/2 cups water and 1/4 tsp. salt; bring to a boil, and cook, covered, 10 to 12 minutes.
To make Dressing: Combine all ingredients except olive oil in bowl. Gradually whisk in oil. Set aside.
To make Salad: Mix barley, 2 1/2 cups water and salt in large saucepan; bring to a boil. Lower heat and cook, covered, 40 to 45 minutes, or until barley is tender and most liquid is absorbed. Transfer to large bowl, and let cool, fluffing to prevent sticking.
Cut peas in half on diagonal. Cook in large saucepan of lightly salted water, or steam them until just tender, about 2 minutes. Drain, and refresh under cold running water.
Add red pepper, carrots, parsley, chives and peas to barley; toss to mix. Drizzle with dressing, and toss well.