In a small saucepan, bring water to a boil. Stir in barley. Reduce heat; simmer, covered, until barley is tender, 10-12 minutes. Remove from heat; let stand 5 minutes., Finely grate enough zest from limes to measure 1 teaspoon. Cut limes crosswise in half; squeeze juice from limes. In a small bowl, whisk lime juice, lime zest, oil, mustard, honey, salt, cumin and pepper until blended., In a large bowl, combine barley, peppers, onion, mango and cilantro. Add dressing; toss to coat. Refrigerate until serving.