Miso Salmon with Asparagus and Carrots

Name: Miso Salmon with Asparagus and Carrots
Ingredients: 1 cup couscous; Kosher salt and freshly ground pepper; 2 ½ teaspoons finely grated ginger (from a peeled 1-inch piece); 1 ½ teaspoons finely grated lemon zest, plus wedges for serving; 2 tablespoons unsalted butter; 1 bunch scallions, white and light-green parts cut into 1-inch pieces, dark-green tops thinly sliced; 4 carrots, peeled and cut on the bias into ½-inch pieces (1 ½ cups); 2 tablespoons white or yellow miso; 4 boneless, skinless salmon fillets (each 1 inch thick); 1 pound asparagus, trimmed