Brush away any dirt from the mushrooms. Cut them in large pieces including the stems. Coat them lightly with olive oil. Sprinkle with salt and lots of pepper.
In a very hot skillet, pour about 1 tablespoon and allow to warm. Add the mushrooms in one layer and sear them. Place them in one layer on a baking sheet. Keep doing this until all the mushrooms are ready for the oven.
Place the mushrooms in a 425 degree oven for about 20-25 minutes. Check on them half way and give them a toss.