Load the Crockpot: Place the chicken breasts at the bottom of a 6-quart or larger slow cooker. Add the chopped onion, carrots, celery, and garlic on top.
Add Liquids & Herbs: Pour the chicken broth over the ingredients. Add the dried thyme, bay leaves, and black pepper.
Slow Cook: Cover and cook on LOW for 6-8 hours or on HIGH for 3-4 hours, until the chicken is cooked through and tender.
Shred Chicken: Carefully remove the chicken from the crockpot and place it on a cutting board. Use two forks to shred the meat into bite-sized pieces. Remove and discard the bay leaves from the soup.
Cook Noodles: While the chicken rests for a moment, cook the egg noodles in a separate pot of salted, boiling water according to package directions. Drain well.
Combine & Serve: Return the shredded chicken to the crockpot. Add the cooked and drained noodles. Stir everything to combine. Taste the soup and season with salt as needed.
Garnish: Ladle the hot soup into bowls and garnish generously with fresh parsley before serving.