Combine pork loin, chestnuts, and the next 9 ingredients (chestnuts through star anise) in a large Dutch oven over medium-high heat, and bring to a boil. Cover, reduce heat, and simmer 1 hour and 20 minutes or until meat is tender, stirring occasionally. Discard cinnamon and star anise.
Combine water and cornstarch, stirring well with a whisk. Add cornstarch mixture to pork mixture, stirring well, and bring to a boil. Cook 1 minute or until thick, stirring constantly. Remove from heat.
Cook noodles according to package directions, omitting salt and fat. Place 1/2 cup noodles into each of 6 bowls; top with 3/4 cup pork mixture. Garnish each serving with sliced green onions, if desired.