1. For the dressing, bring vinegar and sugar to a boil in saucepan; boil 3 minutes until mixture is reduced to 1/3 cup. Whisk in olive oil, salt, garlic and pepper. Set aside.
2. Heat oven to 425 degree F. Scrape gills from mushroom caps and discard. Arrange mushrooms smooth side up on a cookie sheet. Remove 2 tablespoons dressing to a cup and brush over tops of mushrooms. Bake 15 minutes. Cover with foil.
3. Meanwhile, cook barley according to package directions. Add the carrots during the last 3 minutes of cooking time. Slice mushrooms; toss with barley and 1/4 cup of the dressing. Toss salad with remaining dressing. Divide among 4 serving plates; top with barley-and-mushroom mixture. Makes 4 servings.