Remove and discard husks and silks from corn. Place corn and zucchini, cut sides up, on a baking sheet coated with cooking spray. Cut peppers in half lengthwise; remove and discard seeds and membranes. Place peppers, skin sides up, on baking sheet; flatten with palm of hand.
Broil vegetables 5 1/2 inches from heat (with electric oven door partially opened) 15 to 20 minutes or until peppers are charred. Remove peppers from baking sheet, and place in ice water until cool. Broil corn and zucchini 5 additional minutes or until lightly browned, turning often. Let cool. Remove peppers from water; peel and discard skins. Coarsely chop peppers. Cut corn from cob. Slice zucchini into 1/2-inch slices.
Combine barley and water in a large saucepan. Bring to a boil; cover, reduce heat, and simmer 30 minutes or until barley is tender. Drain well.
Combine roasted vegetables, barley, beans, green onions, and cilantro; toss lightly. Combine vinegar and remaining 4 ingredients in a jar; cover tightly, and shake vigorously. Pour vinegar mixture over barley mixture; toss lightly. Let stand 15 minutes before serving.