In a large pot over medium heat, add olive oil and chopped onions. Sauté until translucent (about 3-4 minutes).
Stir in minced garlic and sliced mushrooms, cooking until mushrooms are golden brown (5-7 minutes).
Pour in vegetable broth and add shredded rotisserie chicken. Mix gently to combine.
Reduce heat slightly, then stir in heavy cream, fresh thyme, salt, and pepper. Let simmer for about 10 minutes.
Adjust seasoning as needed before serving.
Ladle into bowls; garnish with extra thyme or cracked pepper if desired.