Preheat your oven to 400°F / 200°C.
In a large bowl, combine the cremini mushrooms, olive oil, dried thyme, salt, and crushed red pepper flakes.
Toss thoroughly to ensure the mushrooms are evenly coated.
Spread the seasoned mushrooms in a single, even layer on a large roasting pan or baking sheet.
Place the pan in the center of the preheated oven and roast for 30 minutes, until the mushrooms are nicely browned and have released their liquid.
Remove from the oven and transfer the hot mushrooms to a serving bowl. Immediately toss with the chopped fresh parsley and balsamic vinegar.
Serve warm or at room temperature.
Don't crowd the pan. Give the mushrooms plenty of space on the baking sheet to ensure they roast rather than steam. Use two pans if necessary for a perfectly browned, caramelized result.
Add fresh herbs and vinegar after roasting.
Tossing the parsley and balsamic with the mushrooms right out of the oven preserves their fresh, vibrant flavors and prevents them from becoming dull during cooking.