Season the chicken with the salt and black pepper and put it in a 6-quart slow cooker.
Add the onion, carrots, celery, garlic, broth, thyme and bay leaf.
Cover and cook on low until the chicken is tender and the vegetables are soft, 5 1/2 to 6 hours.
Move the chicken to a bowl, discard the bay leaf and shred the meat.
Switch the cooker to high, add the egg noodles and cook until tender, 15 to 25 minutes depending on the cooker.
Return the chicken, stir in the lemon juice and taste the soup for salt before serving.