Thoroughly clean the mushrooms and, if they're large, cut in half or quarters; otherwise leave them whole.
In a skillet, heat the olive oil with the garlic clove over medium-high heat. Add the mushrooms and let them brown all over, while loosing some of their natural humidity. Season with salt and freshly ground black pepper.
Cook the pasta in boiling water, seasoned with salt (the amount of time varies but it's mentioned on the package). Drain the water, keeping 2 or 3 tablespoons of it.
Add the cheese to the pasta and stir to melt a little. To make the cheese sauce creamier, add some of the cooking water that you've reserved, if necessary.
Add the mushrooms and serve immediately, garnished with fresh oregano.