Preparation Preheat oven to 375°F. Toss beets with oil in roasting pan. Sprinkle with salt. Cover pan with foil. Roast beets until tender, about 50 minutes. Let beets stand covered at room temperature 20 minutes. Peel beets. Place in bowl; cover and chill at least 1 hour. DO AHEAD Can be made 2 days ahead. Keep chilled. Toss onion, oil, capers, and chives in small bowl. Season to taste with salt and pepper. Thinly slice beets. Arrange beets in concentric circles on each of 6 plates. Mound arugula atop center of beets on each. Spoon onion-caper mixture over. Sprinkle with salt and pepper.
Preparation Preheat oven to 375°F. Toss beets with oil in roasting pan. Sprinkle with salt. Cover pan with foil. Roast beets until tender, about 50 minutes. Let beets stand covered at room temperature 20 minutes. Peel beets. Place in bowl; cover and chill at least 1 hour. DO AHEAD Can be made 2 days ahead. Keep chilled. Toss onion, oil, capers, and chives in small bowl. Season to taste with salt and pepper. Thinly slice beets. Arrange beets in concentric circles on each of 6 plates. Mound arugula atop center of beets on each. Spoon onion-caper mixture over. Sprinkle with salt and pepper.