Soak glass noodles in water until soft. This can take 15 minutes or more so you can make the soup in the meantime to save time. Drain and cut into bite-size lengths.
Heat oil in a pot over medium heat. Add onion and garlic, cook until fragrant and translucent. Add chicken, cook until no longer pink. Season with fish sauce.
Pour chicken broth. Cover with lid and simmer until tender, about 20 to 30 minutes. Remove scum off the surface. Add hot water as needed.
Transfer chicken to a plate. Shred with 2 forks. Discard bones.
Dissolve annatto powder in 1 tablespoon water. Add to the pot and stir. Add carrots, shredded chicken, glass noodles, and the white parts of the napa cabbage. Cook for 2 to 3 minutes. Taste, season with black pepper and salt as needed.
Add the remaining napa cabbage. Simmer until soft. Add more hot water as needed. Transfer to serving bowls and top with choice of garnishes. Enjoy!
Video
Notes
Chicken - you can also use other parts with skin or without skin. The bones and the skin will make the soup more flavorful.
Chicken broth - use homemade or dissolve 2 pieces chicken bouillon in hot water.
Glass Noodles - also known as mung bean or glass noodle bean vermicelli. Available in most Asian stores and online.
Nutrition - toppings, and garnishes not included in the calculation.