Herb Roasted Salmon and Barley Salad

In a medium saucepan, combine the barley, 1 1/2 cups water and 1/4 teaspoon salt and bring to a boil. Reduce heat and simmer, covered, until the barley is tender, 20 to 25 minutes. Drain off any remaining water in the pan and spread the barley on a baking sheet to cool. Meanwhile, in a small bowl, whisk together the lemon juice, mustard, and 1 tablespoon oil. Stir in the parsley, 4 tablespoons dill, and lemon zest. Place the salmon on a foil-lined baking sheet. Spread the herb mixture over the salmon and roast until the salmon is opaque throughout, 10 to 12 minutes. In a large bowl, whisk together the yogurt, lemon juice, remaining dill, remaining 2 tablespoon oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Add the celery, cucumber, and cooled barley and toss to combine. Flake the salmon into large pieces. Divide the arugula among bowls, top with the barley mixture, then the salmon.