Separate the rotisserie chicken meat from the bones. Save the bones and put the meat in the fridge until ready to serve.
Place the onion and ginger in a pan and broil on high for a few minutes, until some charring forms on the outside of the onion.
Heat a skillet to medium-high heat. Add spices and toast for 1-2 minutes. Pour spices into the provided pouch.
Add the chicken bones to a large stock pot. Add 4 quarts of water, the broiled onion and ginger, spice pouch, fish sauce, sugar, and chicken bouillon. Bring to a boil, then reduce to a simmer. Cover and simmer for at least 1 hour.
While the broth is simmering, cook rice noodles according to package directions.
Remove bones, spice pouch, onion, and ginger from the broth. Strain the broth until it is clear. Bring it back to a boil.
To assemble your bowl: add rice noodles, shredded rotisserie chicken, and any desired toppings to the bowl.
Pour hot broth over the top. Add sriracha, hoisin, and lime as desired.