Heat the oven to 200°C/fan 200°C/gas 7. Line a 9-inch square baking pan or cake tin with a big square of foil, large enough to completely enclose the beet roots. Lightly rinse the beet roots to remove any really clumpy dirt and pat them dry. Place them in the foil square and lightly drizzle with olive oil and sprinkle generously with salt and pepper. Fold up the foil and crease to seal. Bake the beets for 60 minutes or until they can be just pierced with a fork. Set aside to cool.
Meanwhile, chop the beet greens into bite-size ribbons. In a large skillet, heat a drizzle of olive oil over medium heat and add the garlic. Cook on low for about 5 minutes or until the garlic is golden and fragrant. Add the chopped leaves and stir to coat with the garlic. Cook on medium-low for about 10 minutes or until the leaves are soft and tender. Remove from the heat.
When the beets are cool, rub them with a paper towel to remove the skin. Then chop into pieces and toss with the cooked greens. Taste and season with salt and pepper to taste. Serve warm or cold.