Soak noodles in warm water. In large saucepan, bring broth, 4 cups water and ginger to boil. Divide pork, bok choy, sprouts, scallions and cilantro among 4 large soup bowls. Divide noodles into 4 portions. A portion at a time, lower noodles in mesh strainer into boiling broth for 1 minute; transfer to soup bowls. When all noodles are cooked, ladle hot broth into bowls. Serve with lime wedges and hot chili oil.