Preheat oven to 400°. Place beets in a 15x10x1-in. baking pan. Drizzle with oil; toss to coat. Roast until tender, 40-45 minutes. Cool slightly., Transfer beets to a blender or food processor. Add juice and vinegar; process until smooth. Refrigerate at least 1 hour. In a small bowl, combine Greek yogurt and chopped tarragon; refrigerate., To serve, divide beet mixture among individual bowls; place a spoonful of yogurt mixture in each bowl. Top with diced peaches and tarragon sprigs.