Preheat the Oven: Set your oven to 350°F (175°C) and grease an 8x8 baking dish.
Sauté the Mushrooms: Heat olive oil in a large skillet over medium heat. Add quartered mushrooms, season with salt and pepper, and sauté until the water evaporates, about 7–9 minutes.
Add Garlic: Stir in minced garlic and cook until fragrant, about 1 minute.
Prepare the Filling: Remove skillet from heat and blend in cream cheese until mushrooms are well-coated. Mix in mozzarella, half of the breadcrumbs, and half of the Parmesan cheese.
Transfer to Baking Dish: Spoon the creamy mushroom mixture evenly into the greased dish.
Prepare the Topping: Combine remaining breadcrumbs, Parmesan, parsley, and melted butter. Sprinkle evenly over the casserole.
Bake: Bake for 25–30 minutes, or until the topping is golden brown and crispy.
Serve: Let the casserole cool slightly before serving hot. Enjoy the creamy, cheesy goodness with every bite!