Place the chicken thighs in the bottom of the slow cooker.
Add the diced onion, sliced carrots, sliced celery, and minced garlic on top of the chicken.
Pour the chicken broth over the ingredients in the slow cooker.
Sprinkle the dried thyme, dried parsley, dried rosemary, salt, and black pepper over the soup.
Add the bay leaf to the slow cooker.
Cover and cook on low for 6 hours, or until the chicken is fully cooked and tender.
Remove the chicken thighs from the slow cooker and shred the meat using two forks, discarding the bones.
Return the shredded chicken to the slow cooker.
Stir in the frozen peas and cook on high for an additional 10 minutes.
Remove the bay leaf and stir in the fresh lemon juice.
Taste and adjust seasoning with additional salt and pepper if desired.
Serve hot.