Heat 1 tablespoon of vegetable oil in a large pot over medium-high heat. Once the oil shimmers, add the onions and ginger, charring them face down for about 4 minutes until they develop a deep blackened exterior.

Carefully add 8 cups of water and all remaining broth ingredients into the pot. Bring to a gentle boil, then reduce to maintain a low simmer for 1.5 hours, skimming off impurities.

Remove the chicken and strain the broth through a fine-mesh sieve into another pot to achieve a smooth, clear liquid. Adjust seasoning as needed with salt.

Prepare toppings by thinly slicing green onions and gathering fresh herbs. Cook rice noodles in a separate pot according to packaging instructions.

Assemble by placing cooked rice noodles in bowls, adding shredded chicken on top, and ladle hot broth over everything. Customize with fresh herbs, lime wedges, hoisin, and sriracha.