Heat the olive oil in a large pot over medium heat.
Add the onion and garlic, sauté until translucent, about 3-4 minutes.
Stir in the carrots and celery, cooking for another 5 minutes.
Add the diced red bell pepper and mixed vegetables, stirring well.
Pour in the chicken broth and bring the mixture to a boil.
Add the shredded chicken, thyme, salt, and pepper, and lower the heat.
Let the soup simmer for about 20 minutes to allow the flavors to meld.
Taste for seasoning; adjust with more salt, pepper, or thyme if needed.
Serve hot, garnished with fresh parsley if desired.