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.