Preheat the oven to 400 degrees. Remove stems from mushrooms, and reserve if they are to be used in the filling. Use a damp cloth or mushroom brush to clean mushrooms. Brush each mushroom with olive oil. Add salt and pepper to taste.
Place mushroom caps, cavity side down, on a baking sheet. Roast until the mushrooms are golden and their liquid begins to seep from the cavity, 6 to 7 minutes. Place cavity side up on paper towels to drain. The mushroom caps can be stored in an airtight container for up to 4 hours.