Pre-heat oven to 450°F.
 Arrange mushrooms in a single layer on a large jelly roll pan and coat with cooking spray; season to taste with salt and pepper. 
 Roast mushrooms for 15 minutes and then turn mushrooms and roast for 5 to 10 minutes more, until cooked through.
 Meanwhile, place garlic and thyme in a large bowl. 
 When mushrooms are done cooking, immediately place in bowl and toss to coat with garlic and thyme. 
 Add vinegar and toss again.