Preheat oven and a baking dish to 220ºC. Remove stems from mushrooms. Place mushrooms cup side up into the hot baking dish. Drizzle each mushroom with a little olive oil and season with salt and pepper.
Place mushrooms into the oven and roast for 8-10 until mushrooms are just tender.
Remove baking dish from oven, crumble over ricotta and sprinkle with mozzarella. Return dish to the oven and bake another 3-4 minutes until cheese is melted.