Season chicken with salt and pepper and bake at 350 degrees for 20-25 minutes until cooked through. Let rest for 10 minutes before slicing or shredding.
Meanwhile, bring stock, fennel, coriander, anise, cardamom, cinnamon sticks, cloves, ginger and soy to a boil. Reduce heat and simmer on medium-low for 20 minutes. Strain spices and return stock to pot.
Bring back to a boil and add rice noodles. Cook according to directions. If you’re making the stock in bulk to freeze, do not add noodles. Add them when you reheat the stock, right before eating.
To serve, add equal portions of chicken, red onion and noodles to each bowl.
Bring stock back to a boil and ladle into soup. Serve with all the garnishes on the side and let people add sprouts, scallions, basil, cilantro, limes and sriracha to their own tastes.