Slice the mushrooms thinly. In a large frying pan, heat the olive oil over medium heat. Add the garlic and parsley, stirring frequently. When the garlic becomes fragrant, about one minute, add the mushrooms; they will absorb the oil and may stick to the pan before releasing their moisture. When the mushrooms start to soften, reduce the heat to low and season with salt and pepper. Continue to cook, stirring occasionally for 15 minutes. Transfer to a serving bowl and serve.