Rinse the mushrooms thoroughly and trim them. Set them round side up and cut downward into slices as thick or thin as you want 1/4 inch thick is a good place to start).
Put the oil in a large skillet over medium heat. When it’s hot, add the mushrooms and sprinkle them with salt and pepper. Cook, stirring occasionally, until the mushrooms have released their liquid, become tender, and the pan is beginning to dry out again, 10 to 15 minutes.
If you want the mushrooms to have a little sauce, pour in 1/2 cup wine. For moist mushrooms without any sauce, stir in 1/4 cup. Let the liquid bubble and evaporate for 1 minute, stirring the bottom of the pan to scrape up any browned bits, then turn the heat down to low.
When the mushrooms are done as you like, stir in the garlic and parsley and cook for just 1 minute more. Taste and adjust the seasoning with salt or pepper and serve hot, warm, or at room temperature.