Cut the stems off the beets and remove the greens from the stems. Cut the stems into 2 inch pieces.
Remove the roots and cut the onions into quarters.
Put the beets and onions on a parchment lined tray. Drizzle 2-3 tbsp of olive oil over the top. Season the onions with salt and pepper. Roast for 1 hour. If your beets are large you may need to roast for an additional 10-15 minutes until very easily pierced with a knife.
In a large pan, saute the thinly sliced beet greens in 2 Tbsp olive oil for 5-6 minutes or until slightly wilted. Season with salt & pepper.
20 minutes before the beets are done, remove the tray from the oven and add the beet stems to the tray. Spray them with a light layer of olive oil and season with salt and pepper. Put the tray back into the oven to finish cooking.
Let the beets cool for at least 10 minutes before you try to peel them.
Put the beet greens down first on a serving dish and top with the sliced beets and roasted onions. Sprinkle the feta cheese over the top. Drizzle the balsamic vinegar over the top right before you serve it hot. Enjoy!