Like Middle Eastern tabbouleh, this salad has a fresh, herby taste.
Bring 5 cups of water to a boil in a medium saucepan. Stir in barley and 1 teaspoon salt. Reduce heat to medium and cook until tender, about 35 minutes. Drain and rinse with cool water. Set aside.
Combine diced tomatoes and cucumbers in a large bowl. Add the barley, celery, scallions, parsley, mint, and cayenne pepper. Toss to combine and set aside.
In a small bowl, whisk together the lime juice, olive oil, remaining 1 teaspoon salt, and freshly ground pepper; add to barley mixture. Toss to combine. Serve immediately or refrigerate for up to 8 hours.