Scatter onion, carrots, celery in slow cooker insert.
Lay chicken breasts over vegetables, season with salt and pepper.
Add garlic, bay leaves, thyme, parsley, then pour broth over everything.
Cover and cook on LOW 4-6 hours or HIGH 2.5-3 hours until chicken shreds easily.
Shred chicken with two forks, discard bay leaves, return to pot.
Stir in dry egg noodles, cook on HIGH 20-30 minutes until tender.
Stir in lemon juice, adjust salt and pepper to taste.
Ladle into bowls, top with fresh parsley, serve immediately.