Load the slow cooker: Add the carrots, celery, onion, and garlic to the bottom.
Place the chicken on top. Sprinkle in thyme, parsley, oregano (if using), and add the bay leaves.
Pour in the broth: Use low-sodium chicken broth so you can control the salt at the end. Cover the slow cooker.
Cook low and slow: Cook on Low for 6–7 hours or on High for 3–4 hours, until the chicken is very tender.
Shred the chicken: Remove the chicken to a cutting board.
Shred with two forks into bite-size pieces. Discard bay leaves.
Add noodles: Stir the shredded chicken back into the slow cooker. Add the egg noodles and cook on High for 15–20 minutes, or until the noodles are just tender.
Stir occasionally to prevent clumping.
Finish and season: Stir in lemon juice and butter or olive oil, if using. Taste and add salt and pepper until the flavors pop.
Serve: Ladle into bowls and top with fresh parsley. Add extra pepper or a squeeze of lemon if you like it bright.