Working with beets scrubbed clean, toss them directly onto the coals, turning them every 5 minutes. The outside will char, while the insides soften in about 20-30 minutes. You can check for doneness by poking them with a knife. When they feel soft inside, remove them from the coals and brush off excess ash. Cut them into 2? chunks, and arrange on a serving platter. Season with olive oil and salt, and serve while warm.