Heat 2 tablespoons of the oil in a large skillet over high heat until hot. Reduce the heat to medium; add the onion and cook, stirring occasionally, until softened, about 5 minutes. Increase the heat to medium high; add the mushrooms and cook, stirring, until the mushrooms have browned and the liquid they release has evaporated, 4 to 5 minutes. Season the mushroom mixture with salt and pepper to taste and transfer it to a bowl; add the chiles and olives and set aside. Wipe out the skillet.