Cut mushroom into slices about 1/2 inch thick each.
Heat cast iron skillet or pan over medium heat & fry the mushroom slices without oil for about 5 minutes, flip them over & cook for 5 minutes more.
Add 1 tbsp olive oil & 1 tbsp vegan butter to the pan, sprinkle with salt & pepper, cook for one minute, flip over, sprinkle with more salt & pepper & serve hot with favorite sauces (I love chimichurri) & sides like beans, rice & roasted veggies.