1. In a Dutch over or soup kettle, heat oil over medium heat, add in onion, celery, and carrots with a pint of salt and cook, stirring frequently until vegetables become tender (~5-8 minutes). Add broth and bring to a boil.
2. Reduce heat to medium-low, add cooked chicken and cauliflower rice. Continue to simmer for ~8-10 minutes, until cauliflower rice is just tender.
3. In a seperate bowl, whisk together the jiuce of 1 lemon with 1 egg. Slowly ladle in ~1 cup of the hot broth, whisking constantly. This technique is called "tempering", to slowly heat the egg before adding it to the hot soup. This prevents the egg from scrambling. Stir the lemon-egg mixture back into the soup.
4. Season with salt and pepper to tast and garnish with fresh parsley.