In separate containers, soak the noodles and mushrooms in warm water for at least 10 minutes. Prepare the other ingredients while it soaks.
In a large saucepan, put the chicken breast, half of the onion (halved), bay leaves, and salt to taste. Cover the chicken with water and boil over medium heat for 20 minutes, or until chicken is cooked. Note: The water will be adjusted depending on size of pan. Ensure the chicken breast is submerged in the water. See note below.
In a large stock pot, add olive oil over low heat. Sauté the other half of the onion (diced), carrots, celery, ginger, and garlic over low heat until softened.
Once the chicken is done boiling, shred the chicken. Add the shredded chicken and the mushroom to the sauté pan. Combine and sauté for 2-3 minutes. For increased flavor, add the water from the boiled chicken breast pan to the sauté pan.
Add the chicken broth, water, lemon juice, fish sauce, and annatto powder. Bring the mixture to a boil. Once boiling, add the noodles. Boil for an additional 5 minutes. Season with additional fish sauce, lemon juice, salt and pepper to taste.
Garnish with toppings if desired when serving. Enjoy!