In a large pot, heat the olive oil over medium heat.

Add the diced onion and sauté until translucent, about 5 minutes.

Stir in the minced garlic and sliced mushrooms, cooking until mushrooms are tender, about 5 minutes.

Pour in the chicken broth, and add the shredded rotisserie chicken, sliced carrots, sliced celery, thyme, salt, and black pepper.

Bring the mixture to a boil, then reduce heat and let it simmer for 20 minutes.

If desired, stir in the heavy cream just before serving for added richness.