2 tablespoons extra-virgin olive oil
1 large onion, finely chopped
Kosher salt and freshly ground black pepper
1 1/2 cups pearled barley
2 sprigs fresh thyme
3 cups low-sodium vegetable broth
1 pound (1 bunch) asparagus, rough stalks trimmed and cut into 1-inch pieces
2/3 cup grated Parmesan
Zest of 1 lemon, plus lemon wedges, for serving
1/4 cup roughly chopped fresh flat-leaf parsley
1/4 cup roughly chopped fresh mint
Heat the oil in a large skillet over medium-high heat. Add the onions, 1/2 teaspoon salt and 1/8 teaspoon pepper, and cook, stirring occasionally, until lightly browned, about 5 minutes. Stir in the barley and thyme, and cook, stirring, until the barley is just golden, about 2 minutes more.
Transfer the barley mixture to a 6-quart slow cooker, and add the broth, 1 1/2 cups water and 1/2 teaspoon salt. Cover, and cook on high until the liquid is absorbed and the barley is tender, about 3 hours.
Discard the thyme, and stir in the asparagus. Return the lid to the pot, and cook until the asparagus is tender, 30 minutes more. Stir in the Parmesan, lemon zest, 1 teaspoon salt and 1/4 teaspoon pepper. Thin out the risotto to the desired consistency with warm water, as needed. Fold in the parsley and mint, and serve with lemon wedges on the side.