Tips: To prepare portobello mushroom caps, gently twist off the stems of whole portobellos. Using a spoon, scrape off the brown gills from the underside of the mushroom caps. If you prefer, purchase portobello mushroom caps, rather than whole mushrooms.
Oiling a grill rack before you grill foods helps ensure that the food won't stick. Holding a folded paper towel with tongs, dip it in vegetable oil and rub it over the rack. (Do not use cooking spray on a hot grill.)