Season the chicken breasts on both sides with salt and pepper and set aside.
Next, add the oil to a large pot over high heat and once it begins to lightly smoke add in the chicken, turn the heat down to medium and cook for 3-4 minutes.
Flip over, turn the heat down to low and cook for 5 minutes and then flip back for a further 5 minutes or until browned and cooked throughout.
Remove the chicken and roughly dice. Set aside.
Add the carrots, celery, onion and garlic to the pot and sweat the vegetables over low heat for 8-10 minutes until tender.
Add the chicken back in along with the rice and chicken stock. Cover and cook over low heat for 25 minutes or until the rice is cooked.
Make the cornstarch and water mixture and mix it into the soup. It will become very thick.
Finish by adding in cream, parsley, salt and pepper.