In a dry skillet, toast the coriander seeds, fennel seeds, star anise, and cinnamon stick until fragrant.

Place the whole chicken in a large pot and cover it with 8 cups of water.

Add the halved onion and sliced ginger to the pot.

Add the toasted spices and fish sauce to the pot.

Bring the pot to a boil, then reduce the heat to low and simmer for about 1 hour.

While the broth simmers, cook the rice noodles according to package instructions.

Once cooked, remove the chicken from the pot and let it cool slightly before shredding the meat.

In serving bowls, layer the cooked noodles, shredded chicken, and ladle the hot broth over the top.