Add the vegetables and chicken to the crockpot. Place the carrots, celery, onion, garlic, and chicken breasts in the slow cooker.
Pour in the broth and seasonings. Add the chicken broth, salt, pepper, dried thyme, dried parsley, and bay leaf.
Stir gently to combine everything.
Cook until the chicken is tender. Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours. The chicken should be fully cooked and easy to shred.
Shred the chicken. Remove the chicken breasts from the crockpot and shred them with two forks. Return the shredded chicken to the soup.
Add the noodles near the end. Stir in the egg noodles and cook for another 15 to 20 minutes, or until the noodles are soft.
Check them often so they do not get mushy.
Finish and serve. Remove the bay leaf, stir in the lemon juice if using, and taste for seasoning. Add more salt or pepper if needed, then top with fresh parsley and serve warm.