Preheat oven at 220°C/430°F. Place radishes cut-side-down on a baking dish, drizzle with olive oil and season with salt and pepper.
Roast for 12-15 minutes until edges are beginning to brown and radishes are fork-tender but still firm. If you prefer them more tender, leave them a few more minutes in the oven. Optional: serve them with lemon and parsley.