Step 1

Trim stems from cremini (break apart oyster mushroom clusters, if using). Put mushrooms in a medium bowl, and set aside.

Step 2

Whisk together lemon juice, vinegar, and oregano in a medium bowl. Whisk in oil in a slow, steady stream; whisk until mixture is emulsified. Whisk in the salt and pepper. Pour marinade over mushrooms, and let stand at room temperature, stirring occasionally, at least 20 minutes; if desired, refrigerate mushrooms in an airtight container overnight. Serve at room temperature.