Remove stems from mushrooms. Wipe mushrooms with a clean, damp cloth or paper towel. Place mushrooms, stemmed sides down, in a shallow baking pan.
Brush or drizzle the mushroom caps with half of the olive oil. Broil mushrooms 3 to 4 inches from the heat for 5 minutes. Remove the pan from the oven. Using tongs, turn the mushrooms over and brush or drizzle with the remaining olive oil. Return to the broiler; broil another 5 to 6 minutes more or until tender.
Remove from the oven. Season to taste with the salt. (Don't salt the mushrooms when broiling, as this will pull some of the flavorful juices from the portobello.) Allow to cool slightly before serving. Makes 4 side-dish servings.