Preheat your oven to 200°C or 320°F
Scrub off the beets really well to get off any sand or dirt that might still be on them. Trim off any leaves that might have come with them when purchased.
Dry them well with a paper towel.
In a square of aluminum foil place the washed beets with a sprinkling of the course salt, close it around the beets making sure the seal is tight. Place in a small roasting pan and place in the middle of a preheated oven.
Roast for approx 50 to 60 minutes. This should be fine for medium size beets.
When done open the package on a plate and let cool for about an 15 minutes so they are cool enough to handle.
With a small peering knife peel off the skin and cut into bite size pieces or slice. I like this a bit chunky but not too big.
Drain off the onions and dry with a paper towel. Break up the feta cheese and sprinkle both over the cut up beets. Then sprinkle over the olive oil and the vinegar, salt and pepper to taste and serve chilled but not cold.