Steamed Ginger Sole with Lemon Soy Sauce

Name: Steamed Ginger Sole with Lemon Soy Sauce
Ingredients: 3 tablespoons soy sauce; 1/2 teaspoon finely grated lemon zest; Juice from 1/2 a lemon; 1 teaspoon toasted sesame oil; 4 bunches scallions, whites and greens separated, thinly sliced; 1/2 teaspoon finely grated peeled fresh ginger; 4 (6-ounce) sole or other flat fish fillets; Kosher salt and freshly ground black pepper; 4 large Napa cabbage leaves; 1 medium carrot, thinly sliced on the bias; 8 shiitake mushroom, stems trimmed and discarded