1. Preheat the oven to 375°F. Grease a baking sheet with nonstick spray.

2. In a large bowl, toss the mushrooms with the olive oil, vinegar, salt and pepper to combine.

3. Pour the mushrooms onto the prepared baking sheet, then spread them out evenly (don't overcrowd or they won't get crispy). Roast until the mushrooms are very brown and crisp, 40 to 45 minutes.

4. Let the mushrooms cool slightly, then garnish with parsley and flaky salt, if using. You can serve the mushrooms warm or at room temperature.