Preheat oven to 450. Spray a cooking sheet or roasting pan. (To lessen the mess, consider lining it with parchment paper instead.) Place mushrooms gill-side up on the pan. Sprinkle with a little salt and pepper. Roast until tender, about 20 minutes.
Meanwhile, combine breadcrumbs, Parmesan, parsley, oil, 1/8 t. salt and some pepper. Remove mushrooms from oven. Top each with 2 T. of crumb mixture, spreading evenly. Return to oven and cook until browned, about 5 minutes.