Rehydrate the rice noodles according to the instructions on the packaging. Drain.
In a large saucepan, heat the oil over medium heat. Cook the onion and shiitakes for 3 to 4 minutes. Keep warm on a plate.
In the same saucepan, cook the garlic and ginger for 1 minute. Add salt and pepper.
Add the stock, soy sauce, fish sauce and star anise. Bring to a boil, then let it simmer on low heat for 15 to 20 minutes. Take out the star anise and throw it away.
Add the bok choy and shrimp to the pan. Continue cooking for 2 to 3 more minutes. Take them out with a slotted spoon.
Share the bok choy, cooked shiitakes, rice noodles and shrimp between four bowls. Pour over the hot broth. Garnish with spring onion and coriander.