Heat olive oil in a large pot over medium heat. Add diced onion, sliced carrots, and chopped celery. Sauté, stirring occasionally, until the vegetables are soft and fragrant, about 8 minutes.
Add minced garlic to the vegetables and cook for another minute until it becomes fragrant and slightly golden.
Pour in the chicken broth and bring it to a gentle simmer. Add the shredded cooked chicken and sprinkle in the chopped herbs. Let the soup simmer gently for 20 minutes, allowing flavors to meld.
Taste the broth and season with salt and pepper as needed. Stir in the fresh lemon juice to brighten the flavors, and cook for another 2 minutes.
Ladle the hot soup into bowls, garnishing with additional chopped parsley if desired. Serve immediately, enjoying the vibrant aroma and comforting warmth.