Preheat your oven to 425°F (220°C).
Wash and trim the radishes, then cut them in half. If they are exceptionally large, you can quarter them for even cooking.
In a medium bowl, toss the halved radishes with olive oil, salt, and black pepper until well coated.
Spread the radishes in a single layer on a baking sheet. Place them cut-side down to promote the best browning and caramelization.
Roast for 15 to 20 minutes, or until the radishes are crisp-tender and lightly browned around the edges.
While the radishes roast, prepare the dip. In a small bowl, whisk together the plain Greek yogurt, minced garlic, chopped fresh chives, and lemon juice.
Transfer the warm roasted radishes to a serving platter and serve immediately, either drizzled with the garlic chive yogurt or with the sauce on the side for dipping.