Place a large pot over medium heat and pour in the chicken stock, bringing it to a gentle simmer.
Add the boneless chicken thighs to the simmering broth, cooking for about 10 minutes until they are just cooked through and tender, with the broth starting to smell savory.
While the chicken cooks, chop the carrots and celery into uniform pieces for even cooking, and thinly slice the onion.
Remove the chicken from the broth and set aside to rest briefly. Toss the chopped vegetables into the pot and cook for 5–7 minutes, until they soften slightly but retain some crunch.
While the vegetables simmer, shred the cooked chicken into bite-sized pieces using two forks.
Return the shredded chicken to the soup, stirring well to combine, and let it simmer for another 5 minutes to meld the flavors.
Stir in the lemon juice and season with salt and pepper, tasting and adjusting the seasoning to your preference.
Sprinkle the chopped fresh herbs over the soup just before serving to add a bright aroma and fresh flavor.
Serve hot, with a slice of crusty bread if desired, and enjoy the vibrant, comforting bowl of chicken soup.