Preheat the oven to 350°F (175°C).
Cook the chicken if not already cooked, then shred or dice it.
Heat olive oil in a large skillet over medium heat. Sauté sliced mushrooms for 5 minutes until golden brown.
Add minced garlic to the mushrooms and cook for an additional 1-2 minutes until fragrant.
In a large mixing bowl, combine cooked chicken, sautéed mushrooms, heavy cream, chicken broth, cheddar cheese, Parmesan cheese, thyme, onion powder, salt, and pepper. Mix well.
Transfer the mixture into a greased 9x13-inch baking dish and spread evenly.
Bake in the preheated oven for 25-30 minutes until bubbly and golden brown.
Let cool for a few minutes, then garnish with fresh parsley before serving.