Heat the olive oil in a large pot over medium heat. Add the diced onion, sliced carrots, and celery. Cook for about 5 minutes, stirring occasionally, until the vegetables begin to soften and release their aroma.

Add the minced garlic, chopped zucchini, and green beans to the pot. Stir and cook for another 1 to 2 minutes, just until the garlic is fragrant.

Place the chicken directly into the pot. Pour in the chicken broth and add the diced tomatoes, dried thyme, dried parsley, salt, and black pepper. Stir to combine.

Bring the soup to a gentle boil, then reduce the heat to low. Let it simmer uncovered for 25 to 30 minutes, or until the chicken is fully cooked and tender.

Remove the chicken from the pot and shred it using two forks. Return the shredded chicken to the soup and stir well.

Taste and adjust seasoning as needed. Stir in the lemon juice if using, then let the soup simmer for another 5 minutes.

Ladle the soup into bowls, garnish with fresh parsley, and serve hot.