Preheat the oven to 425°F (220°C)
Clean the mushrooms with a damp paper towel
Trim the stems if needed
Leave small mushrooms whole
Halve or quarter larger mushrooms
Toss mushrooms with olive oil
Add salt and black pepper
Add garlic, thyme, or rosemary if desired
Spread mushrooms in a single layer on a baking sheet
Do not overcrowd the pan
Roast for 20 to 25 minutes
Stir or flip halfway through
Roast until browned and tender
Serve immediately