Remove the skin and bones from the rotisserie chicken, shred the meat into bite-sized pieces, and set aside.
In a dry pan over medium-low heat, toast the spices until they become fragrant, about 3 minutes. Transfer them into a mesh spice bag for easy removal later.
In a large pot, place the onion (cut-side down) and ginger, charring them until slightly blackened and aromatic.
Add the chicken carcass and any remaining scraps to the pot. Pour in approximately 8 cups of chicken broth or water.
Bring to a boil, then reduce the heat and simmer for 45 minutes to an hour to extract the flavors. Strain the broth using a fine mesh strainer or cheesecloth into another large pot, discarding the solids.
Return the strained broth to the stove, bringing it back to a simmer. Add fish sauce, salt, sugar and chicken bouillon. Taste and adjust as needed.
Prepare the rice noodles according to the package instructions. Once cooked, drain and rinse them under cold water to prevent overcooking.
Divide the cooked rice noodles evenly into serving bowls. Top with the shredded rotisserie chicken.
Ladle the hot broth over the noodles and chicken, ensuring everything is well covered.
