1. Heat oven to 325 degrees F. Combine five-spice powder and salt in a cup; sprinkle over chicken. Heat oil in medium Dutch oven over medium-high heat 1 minute. Add chicken skin side down. Cover and cook about 6 minutes or until golden brown, turning once. Transfer chicken to small baking dish. Discard drippings.
2. Bake chicken 12 to 15 minutes, until an instant-read thermometer reaches 170 degrees F when inserted in center of each breast.
3. Meanwhile, combine miso paste, soy sauce, and 1/4 cup of the broth in small bowl. Heat same Dutch oven over medium heat; add garlic and ginger and cook 1 minute. Stir in remaining broth and miso mixture until smooth. Add carrot and bring mixture to boil; cover and simmer 15 minutes. Add bok choy and tofu. Cook uncovered 5 minutes more, until bok choy is just tender and tofu is heated through. (If using fresh spinach, cook 2 minutes.)
4. Slice each chicken breast crosswise into 6 diagonal pieces. Divide noodles among 4 bowls. Ladle soup over noodles and top with chicken. Makes 4 servings.