01 - Heat olive oil in a large soup pot over medium heat. Add diced onion, sliced carrots, and celery. Sauté for 5 minutes until vegetables begin to soften and onion becomes translucent.
02 - Stir minced garlic into the vegetable mixture and cook for 1 minute, stirring constantly to prevent burning. Garlic should become fragrant but not browned.
03 - Add chicken pieces to the pot. Cook, stirring occasionally, until chicken is lightly browned on all sides, approximately 3 to 4 minutes.
04 - Pour in chicken broth. Add dried oregano, thyme, basil, bay leaf, red pepper flakes if using, salt, and black pepper. Stir well to combine and bring mixture to a gentle boil.
05 - Reduce heat to low, cover pot, and simmer for 15 minutes. Chicken should be cooked through and vegetables tender when pierced with a fork.
06 - Stir in chopped spinach, lemon juice, and lemon zest. Simmer uncovered for 2 to 3 minutes, just until spinach wilts completely.
07 - Remove pot from heat. Discard bay leaf. Stir in fresh parsley. Taste soup and adjust salt and pepper seasoning as needed.
08 - Ladle hot soup into individual serving bowls. Garnish with additional fresh parsley and an extra squeeze of lemon juice if desired.