Bring A Large Pot Of Lightly Salted Water To A Boil. Place The Penne Pasta In The Pot, Cook For 8 To 10 Minutes, Until Al Dente, And Drain. Heat The Oil In A Large Skillet Over Medium Heat, And Cook The Garlic And Mushrooms Until Mushrooms Are Tender. Season With Salt And Pepper, And Mix In The Butter. In A Large Bowl, Toss The Cooked Pasta And The Mushroom Mixture. Sprinkle With Parmesan Cheese And Garnish With Parsley To Serve.