Warm Cauliflower and Herbed Barley Salad

Place barley in a large saucepan; add water to cover by 2". Season with salt. Bring to a boil and cook until tender, 25-30 minutes. Drain; run under cold water. Set aside.

Meanwhile, whisk lemon juice, mayonnaise, Dijon mustard, and 5 tablespoons oil in a medium bowl until emulsified. Season dressing with salt and pepper; set aside.

Heat remaining 1 tablespoon oil in a large skillet over medium heat. Add cauliflower; cook, turning occasionally, until browned in spots, 10-12 minutes. Add 2 tablespoons water, cover, and cook until just tender, about 2 minutes longer. Season with salt and pepper.

Transfer cauliflower to a large bowl; add beans, 1/4 cup parsley, 1 tablespoon tarragon, reserved barley, and half of reserved dressing. Toss to coat; season with salt and pepper.

Divide salad among bowls; drizzle remaining dressing over. Garnish with lemon zest, 1/4 cup parsley, and 1 tablespoon tarragon.