Chop the onion, carrots, and celery into uniform pieces. Mince the garlic and set all aside.
Place a heavy-bottomed pot over medium heat. Add a splash of oil, then toss in the diced onion, carrots, and celery. Sauté until vegetables soften and turn fragrant, about 8 minutes, with gentle stirring.
Add the minced garlic and fresh herbs (parsley and thyme) to the pot. Cook for about 30 seconds to 1 minute until fragrant, stirring constantly to prevent burning.
Pour in the chicken broth and bring the mixture to a gentle simmer. Skim off any foam that rises to keep the broth clear, about 2-3 minutes.
Add the shredded cooked chicken and bay leaves to the broth. Season with salt and pepper, then let the soup simmer uncovered for 10 minutes to meld the flavors and heat through.
Taste the soup and adjust seasoning as needed. Squeeze in fresh lemon juice to brighten the flavor and sprinkle chili flakes if you like a gentle heat.
Remove the bay leaves and ladle the hot soup into bowls. Garnish with additional parsley if desired, and serve immediately for a nourishing, comforting meal.