Bring a large pot of water to a boil over high heat. Add barley and 1 teaspoon salt. Reduce heat to medium and cook until barley is tender, about 35-40 minutes. Drain and set aside.
Meanwhile, whisk shallot, mustard, lemon juice and olive oil together in the bottom of a serving bowl. Add the warm barley and herbs and stir to combine. Season to taste with salt and pepper and additional lemon juice. Serve warm.