Trim stump on muchroom. Place portabella mushroom fin side up in baking sheet. Rub with olive oil and roast in oven at 350 for 10-15 minutes. Remove from oven and spoon on spaghetti sauce top with provolone or motzerella cheese. Add additional cooked toppings (garlic, onions, bacon, etc.) Put back in oven until cheese melts. Serve with a green salad and garlic bread. Yummy!!