If you'd like to grill the mushrooms instead of pan-frying them, marinate 3 whole portobello mushrooms and grill them for about 5 minutes on each side. Then, cut each mushroom into slices AFTER they are cooked.  To roast the mushrooms instead of pan-frying, add them in a single layer to a baking sheet covered in parchment paper. It's really important to use parchment paper or else the mushrooms will stick to the pan. Then, roast them at 400F for around 10-15 minutes until cooked through.