Place the chicken breasts in the bottom of the slow cooker.
Add the diced onion, carrots, celery, and minced garlic on top of the chicken.
Pour in the chicken broth and sprinkle the dried thyme, dried oregano, black pepper, and salt over the ingredients.
Cover and cook on low for 5 to 6 hours, or until the chicken is cooked through and vegetables are tender.
Remove the chicken breasts from the slow cooker and shred them using two forks.
Return the shredded chicken to the slow cooker.
Add the orzo pasta to the slow cooker and stir to combine.
Cover and cook on high for an additional 20 to 25 minutes, or until the orzo is tender.
Stir in the fresh parsley and lemon juice.
Taste and adjust seasoning with additional salt and pepper if needed.
Serve hot.