Heat a large heavy-bottomed Dutch oven or pot over medium heat. Add the coconut oil and onion to the skillet and mix well to combine. Cook the onions for 5-6 minutes, or until softened and translucent. Stir frequently.
Reduce heat to medium-low. Add the white parts of the green onions, minced garlic, and ginger, and cook for 1 minute, stirring continuously to prevent burning. Add the Thai red curry paste and cook for another minute, stirring continuously.
Add the chicken broth and water. Increase heat to high and bring to boil, then reduce heat to a simmer and add the chicken breasts.
Cover and cook over low heat until the chicken is cooked though, approximately 20 minutes. Use kitchen tongs to remove the chicken pieces from the pot and transfer them to a clean cutting board to cool. Shred with a fork once cool enough to handle.
Add the lime juice, fish sauce, soy sauce, brown sugar, and coconut milk to the pot. Mix well to combine and season with salt, to taste. Add the baby bok choy and simmer, altogether, for 10-15 minutes.
Meanwhile, cook the rice noodles separately and according to package instructions. Strain and set aside until ready to serve (if your noodles stick together, rinse with cool water).
Return the shredded chicken back to the pot.
Serve each bowl with the desired amount of noodles. Ladle hot soup over the top and garnish with fresh mint, basil, cilantro, lime juice, and fish sauce, if desired.