Preheat oven to 425 degrees F. In a medium bowl toss radishes with 1 tablespoon of the olive oil. Place the radishes in a 15x10x1-inch baking pan. Roast, uncovered, for 30 to 35 minutes or until tender and lightly browned, stirring once.
For chive vinaigrette, in a screw-top jar combine the remaining 2 tablespoons olive oil, the white wine vinegar, chives, mustard, pepper, and salt. Drizzle vinaigrette over radishes; toss to coat.