Heat olive oil in a large pot and cook onions, carrots, and celery until softened. Add garlic last to prevent burning. This creates a flavorful base for the soup.
Add chicken breasts and chicken broth, then bring to a gentle boil. Let chicken cook until tender and fully cooked. This step infuses broth with savory chicken flavor.
Remove cooked chicken and shred using two forks. Return shredded chicken to the pot so every spoonful has protein. The soup becomes heartier after shredding.
Stir in couscous, oregano, thyme, salt, and pepper. Couscous cooks quickly and absorbs flavors. Let soup simmer briefly until couscous becomes tender.
Stir in lemon juice, zest, and spinach just before serving. Spinach wilts quickly while lemon brightens flavor. Taste and adjust seasoning if needed.
Top with fresh parsley and optional chili flakes before serving. Serve warm while flavors are vibrant. Enjoy immediately for best texture and taste.