01 - Heat olive oil in a large soup pot over medium heat. Add onion, carrots, and celery. Sauté for 5 minutes, until softened and fragrant.
02 - Stir in minced garlic and cook for 1 minute, being careful not to burn or brown the garlic.
03 - Add chicken pieces to the pot and cook, stirring occasionally, until lightly browned on all sides, about 3 to 4 minutes.
04 - Pour in chicken broth. Add oregano, thyme, basil, bay leaf, red pepper flakes if using, salt, and pepper. Bring mixture to a gentle boil.
05 - Reduce heat to low, cover, and simmer for 15 minutes, until chicken is cooked through and vegetables are tender.
06 - Stir in chopped spinach, lemon juice, and lemon zest. Simmer uncovered for 2 to 3 minutes, just until spinach wilts.
07 - Remove from heat. Discard bay leaf. Stir in fresh parsley. Taste and adjust seasoning with additional salt and pepper as needed.
08 - Ladle soup into bowls. Garnish with extra fresh parsley and an additional squeeze of lemon juice if desired.