Asian Vegetable Soup with Noodles

Name: Asian Vegetable Soup with Noodles
Ingredients: 1 tablespoon cooking oil; 6 scallions including green tops, chopped; 4 cloves garlic, minced; 2 teaspoons chopped fresh ginger; 1/4 cup soy sauce; 1/4 teaspoon dried red-pepper flakes; 3 1/2 cups water; 3 1/2 cups canned low-sodium chicken broth or homemade stock; 4 carrots, cut diagonally into 1/4-inch slices; 3/4 pound napa (Chinese) cabbage (about 1/2 head), leaves shredded (about 3 cups); 3/4 teaspoon salt; 1 small head bok choy (about 3/4 pound), stalks halved lengthwise and cut crosswise into 1/2-inch pieces, leaves shredded; Grated zest of 1 lemon; 2 tablespoons lemon juice; 1/4 pound vermicelli; 1 1/2 teaspoons Asian sesame oil