Heat the olive oil in a large pot over medium heat.
Add the chicken and cook for 5 to 6 minutes until lightly browned. Transfer to a plate.
In the same pot, add the onion, carrots, and celery. Cook for 4 to 5 minutes until softened.
Stir in the garlic and cook for 30 seconds until fragrant.
Add the diced tomatoes, chicken broth, Italian seasoning, thyme, salt, and black pepper. Bring to a boil.
Return the chicken to the pot and reduce the heat to a simmer.
Stir in the green beans, broccoli, and zucchini. Simmer for 12 to 15 minutes until the vegetables are tender and the chicken is fully cooked.
Stir in the chopped parsley and lemon juice, if using.
Taste and adjust the seasoning if needed.
Serve hot with crusty bread or crackers.