Warm a heavy-bottomed pot over medium heat and add a splash of olive oil, allowing it to shimmer and smell fragrant.
Add chopped onion, carrots, and celery to the pot. Sauté, stirring occasionally, until the vegetables are tender and fragrant, about 8 minutes, and the onions are translucent.
Toss in the shredded cooked chicken and stir for about a minute, letting the flavors mingle and the chicken warm through.
Pour in the chicken broth and bring the mixture to a gentle simmer, watching for small bubbles to form around the edges.
Add dried thyme and bay leaves to the broth. Reduce the heat to low and let it simmer uncovered for 20-30 minutes, allowing the flavors to develop and the broth to clarify to a rich golden hue.
Taste the broth and adjust salt and pepper as needed. Remove the bay leaves and discard.
Finish by zesting and juicing a lemon into the soup, giving it a bright, fresh zing that balances the savory flavors.
Give the soup a gentle stir, ensuring all ingredients are well combined and heated through.
Serve hot, ladling the clear, golden broth with tender vegetables and shredded chicken into bowls. Enjoy the comforting warmth and fresh brightness of this simple, nourishing soup.