Preheat the oven to 375°F (190°C).
Heat olive oil in a skillet over medium heat. Sauté the mushrooms until browned, about 6-8 minutes.
Add minced garlic to the skillet and sauté for an additional 1-2 minutes until fragrant.
In a large bowl, combine the shredded chicken, sautéed mushrooms and garlic, heavy cream, cheddar cheese, onion powder, thyme, salt, and pepper.
Pour the mixture into a greased casserole dish, spreading it evenly.
Bake for 25-30 minutes until bubbly and the top is golden brown.
Let it cool for 5-10 minutes before serving.