Herbs and Dijon mustard provide brightness and bite in this barley dish. Use any type of tender green herbs you have on hand, such as basil, mint, chives, parsley, or dill.
Bring barley and 3 cups water to a boil. Add 1/2 teaspoon salt. Reduce heat, cover, and simmer until barley is tender, about 40 minutes. Drain if necessary.
Meanwhile, place shallot in a large bowl, and whisk in mustard, oil, 3/4 teaspoon salt, and 1/2 teaspoon pepper.
Stir in barley and herbs. Serve warm.