Preheat oven to 400°F/200°C. Brush a baking dish or rimmed tray with olive oil.
Add radishes to prepared baking dish, drizzle with olive oil, thyme (optional), and season with salt and freshly ground black pepper to taste. Roast for 45-60 minutes, until golden and crisp, tossing them about half way through.
Sprinkle Parmesan cheese on top and roast for 5 more minutes. Serve right away.
*Daikon radishes work great too! Simply thinly slice them and make sure they're evenly coated with olive oil. Please note that nutrition facts are estimated for a 50g serving of raw radishes (about 10 medium radishes).