Prepare the simple dressing by whisking the vinegar with the oil, salt and pepper.
In a meanwhile, cook the barley as recommended on the package (usually it takes about 20 minutes of cooking in water). Drain.
Preheat oven to 210-215 degrees C. (420-430 degrees F). Wrap each beet up in a piece of foil (better in a double layer). Place on a baking tray and roast for approximately 50-60 minutes. Check with a wooden stick - if it goes through the beets easily, they are ready. Otherwise, cook them for an additional 10-15 minutes or until ready. Cool then peel and dice.