Load the crockpot: Add the chicken, carrots, celery, onion, garlic, broth, thyme, bay leaf, salt, and pepper. Stir to combine.
Cook: Cover and cook on low for 6-7 hours or high for 3-4 hours, until the chicken is tender and the vegetables are soft.
Shred: Remove the chicken, shred it with two forks, and return it to the pot. Discard the bay leaf.
Add the noodles: Stir in the egg noodles, cover, and cook on high for 20-30 minutes, until the noodles are tender.
Finish: Stir in the parsley and lemon juice if using, taste for salt, and serve.
Notes
Add the egg noodles only in the final 20-30 minutes, never at the start, or they turn to mush and soak up the broth. Store noodles separately for best leftovers.