Sauté Aromatics: In a large pot, heat olive oil over medium heat. Add chopped onion and cook until translucent (about 5 minutes). Stir in minced garlic and cook for an additional minute until fragrant.
Add Vegetables: Next, add sliced carrots, celery, and bell pepper. Sauté the vegetables for about 5-7 minutes, allowing them to soften slightly.
Combine with Chicken and Broth: Add the shredded chicken, chicken broth, thyme, oregano, salt, and pepper to the pot. Bring the mixture to a simmer, allowing the flavors to meld together (this should take about 10 minutes).
Add Greens: Stir in the fresh spinach or kale and allow it to wilt (about 2-3 minutes). For an extra zest, squeeze in the lemon juice before serving.
Serve and Enjoy: Ladle the soup into bowls and garnish with fresh parsley if desired.