Preheat the oven to 400 degrees F (200 degrees C).
Clean mushrooms with a damp paper towel and gently remove and discard stems.
Drizzle oil into a large cast iron skillet to evenly coat. Place mushrooms into the skillet, cap-side down. Carefully sprinkle garlic into the mushroom cavities, taking care not to sprinkle directly into the skillet. Drizzle mushrooms with melted butter, then season with salt and pepper.
Roast in the preheated oven for 15 minutes. Sprinkle with Parmesan cheese and return to the oven for 3 to 5 more minutes. Remove from the oven and sprinkle with parsley. Let cool slightly before serving.