Snap off ends of asparagus stalks. Peel asparagus stalks with a vegetable peeler; cut into 1 1/2-inch lengths. Steam until just tender, about 3 minutes. Set aside.
Bring broth to a simmer in a saucepan or in the microwave; keep warm. Heat oil in a heavy, wide pan over medium heat. Add scallions and shiitakes and cook, stirring occasionally, until tender, 3 to 4 minutes. Add barley and stir for 1 minute. Add wine and stir until evaporated, about 1 minute.
Add about 1/2 cup of the hot broth and cook, stirring frequently, until most of the liquid has been absorbed. Continue cooking, adding enough broth, 1/2 cup at a time, and stirring frequently, until the barley is just tender and the mixture has a slightly saucy consistency, about 10 minutes. Remove from the heat and stir in the cheese, herbs, garlic powder and the reserved asparagus. Season with salt and pepper and serve.