Heat the oil in a large soup pot or Dutch oven over medium heat. Add the onion, carrots and celery and cook until softened, about 5 minutes. Add the garlic and cook for 30 seconds more. Add the chicken stock, chicken breasts, herbs and bay leaf and bring to a boil. Once boiling, reduce the heat to medium low and simmer for 20-30 minutes or until a meat thermometer inserted into the thickest part of the breast registers 165 degrees.

Remove the pot from heat and transfer the chicken breasts to a cutting board. Shred or cut the chicken into bite sized pieces and place back in the pot. Add the spinach, lemon juice and season with salt and pepper, to taste. Enjoy!