Place the seasoned chicken breasts in the slow cooker, laying them flat at the bottom.
Add the chopped carrots, sliced celery, and roughly chopped onion around the chicken, spreading them evenly.
Pour the chicken broth over the ingredients, just enough to cover them, and add herbs if using dried thyme or a bay leaf.
Cover the slow cooker and cook on low for about 6 to 7 hours, or on high for 3 to 4 hours, until the chicken is tender and easily shredded.
Remove the cooked chicken from the slow cooker onto a plate, let it cool slightly, then shred it into bite-sized pieces using two forks.
Return the shredded chicken to the slow cooker, stirring it into the broth and vegetables.
About 20 minutes before serving, add the wide egg noodles into the broth, gently stirring to submerge them.
Continue cooking until the noodles are tender, about 15-20 minutes, checking periodically to prevent overcooking.
Taste the broth and adjust seasoning with salt and pepper as needed. Stir in fresh herbs if desired.
Once the noodles are tender and the flavors meld, turn off the slow cooker and let the soup rest for a few minutes.
Ladle the steaming, fragrant chicken noodle soup into bowls, garnish with additional herbs if you like, and serve hot.
