Recipe Credit: Eating Well.com
Photo Credit: Rachel Marek
Position racks in upper and lower thirds of oven: preheat to 450°F.
Wipe mushrooms clean and trim stems flush with caps. Score a 1/4-inch X across the cap of each mushroom. Place the mushrooms in a large bowl. Add oil, garlic powder, salt and pepper; toss until the oil is absorbed. Arrange the mushrooms, stem-side down, on a large rimmed baking sheet. Roast on the lower rack until browned and very soft, 18 to 20 minutes.
When the mushrooms are done roasting, remove them from the oven and turn the broiler to high. Turn the mushrooms stem-side up on the pan and use the bottom of a mason jar or sturdy glass to flatten each mushroom. Drizzle with vinegar and sprinkle with Parmesan. Broil on the upper rack until the mushrooms are crisped on the edges and the cheese has melted, 2 to 4 minutes.