Add oil to large pot and put the onion in cut side down and the smashed ginger slices. Let them cook undisturbed for about 5 minutes until they are a bit brown. (See notes for slow cooker and Instant Pot methods.)
Add cardamom, cinnamon stick, coriander seeds, star anise, and cloves. Cook for about a minute to allow the spices to toast.
Add the apple, cilantro, fish sauce, and sugar and stir together. Add the chicken, then pour the water over it all.
Cover, bring to a boil, then simmer for 1-1½ hours. Truth is, I like to start it early in the afternoon and let it simmer all afternoon! It doesn't hurt the quality of the chicken and it allows all the flavors to really meld.
When the chicken is done, remove it from the broth to let it cool enough to handle. Remove the skin, then separate the meat from the bones and tear it into shreds. Return the chicken to the broth and bring it back to a high temperature.
Prepare the noodles according to the package instructions.
Divide noodles into bowls, add some broth and chicken, then top with any or all of the toppings that you like! Drizzle with hoisin sauce and sriracha.