Preheat the oven to 450 degrees. Place whole and unpeeled beets in a foil packet in a single layer. Roast in the oven for 1 – 1 /12 hours until just tender. You don’t want mushy beets. When beets are cooled, peel off skin with your hands and slice.
Layer beets, onion, basil and avocado on a plate. Sprinkle with feta cheese. Drizzle with lemon juice and olive oil. Season with salt and pepper.