Heat oil in a large skillet over medium-high until just beginning to smoke. Arrange mushrooms in skillet in a single layer and cook, undisturbed, until bottom side is golden brown, about 3 minutes. Make sure the mushrooms are in a single layer, so they get the lovely browned color. If they are too crowded, the mushrooms will steam and won’t brown. Season with salt and pepper, toss mushrooms, and continue to cook. Keep tossing often and, if needed, reduce heat to avoid scorching the mushrooms. Cook until they are golden brown on all sides, about 5 minutes more.