Shrimp and Noodle Stir Fry

Name: Shrimp and Noodle Stir Fry
Ingredients: 6 ounces bean thread noodles (preferably 1/8 to 1/4 inch wide); 3 tablespoons peanut or vegetable oil; 1 medium onion, thinly sliced; 1 teaspoon minced peeled fresh ginger; 1/2 teaspoon dried hot red pepper flakes; 12 fresh shiitake mushrooms, coarse stems removed and caps halved; 4 heads baby bok choy (1pound total), leaves removed and bulb cut into thin wedges; 4 scallions, cut diagonally into 1-inch pieces; 1 pound large shrimp, shelled; 2 cups chicken broth; 2 garlic cloves, minced; 1 tablespoon Asian sesame oil; 1 small jícama (1 pound), peeled and cut into 2-inch-long julienne; 1/2 cup fresh cilantro leaves; Accompaniment: lime wedges