Herbs and Dijon mustard provide brightness and bite in this barley dish.
Whisk together mustard, lemon juice, and 1 teaspoon salt in a small bowl. Add oil in a slow, steady stream, whisking until combined. Set vinaigrette aside.
Preheat oven to 425 degrees. Spread barley on a rimmed baking sheet. Toast in oven until dark brown and fragrant, about 5 minutes. Let cool slightly.
Put 3 quarts water, the stock, bay leaf, crushed red pepper, and 2 teaspoons salt into a large saucepan. Bring to a boil. Add barley. Reduce heat; simmer until barley is tender and chewy, about 1 hour 10 minutes. Drain off excess liquid; discard bay leaf. Transfer barley to a medium bowl. Add vinaigrette; stir. Let cool slightly.
Preheat a grill to medium-high (if you are using a charcoal grill, coals are ready when you can hold your hand 5 inches above grill for just 3 to 4 seconds). Lightly brush asparagus with oil. Season with salt and pepper. Grill asparagus, turning occasionally, until tender, 5 to 6 minutes. Transfer to a plate; let cool slightly. Cut on the diagonal into 3/4-inch pieces.
Add asparagus, oranges, scallion, parsley, and chervil to barley; stir to combine. Season with salt and pepper.