Heat oil in a cast iron skillet on medium-high heat. Add chicken and brown both sides and season with salt and pepper. Cook the chicken until the juices run clear.
Heat a large stock pot on medium heat on top of the stove. Add the remaining oil. Add carrots, celery and onion to the stock pot & stir to coat with oil. Cook for 8 minutes, stirring occasionally.
Add the chicken stock, water and a bay leaf. Adjust heat to high and bring soup to a boil. Once boiling, adjust heat to a medium-low temperature and simmer soup for 8 minutes.