Preheat your oven to 375°F (190°C). Grease a 9x13-inch casserole dish with butter or cooking spray.

In a large skillet over medium heat, add the olive oil. Once hot, add the sliced mushrooms and sauté for 5-7 minutes until golden brown and they have released their moisture.

Add the minced garlic to the skillet and cook for 1-2 minutes until fragrant, stirring constantly to prevent burning.

In a large mixing bowl, combine the cooked chicken, sautéed mushrooms and garlic, heavy cream, dried thyme, oregano, salt, and pepper. Mix until everything is well combined.

Transfer the mixture into the greased casserole dish, spreading it evenly across the bottom.

Sprinkle the shredded mozzarella and grated Parmesan cheese generously on top of the chicken mixture.

Place the casserole in the preheated oven and bake for 25-30 minutes, or until the cheese is bubbly and golden brown. For extra crispy topping, broil for 2-3 minutes at the end, watching carefully.

Remove from the oven and let cool for 5 minutes. Garnish with freshly chopped parsley before serving hot.