Peel the beets and grate (coarsely). Finely chop the greens (leaves and stems). Place all in a large pot, add the water or vegetable stock, lemon juice, cover and bring to the boil. Simmer for 5 minutes, then remove from the heat and leave to cool completely.
Once the beet mixture has cooled add the remaining ingredients, season to taste and stir thoroughly. Refrigerate for at least 30 minutes (up to 4 hours) before serving.
Use either water or vegetable stock (if you use the latter do not season until the soup is ready).
You can use either Greek or natural yogurt, combined with kefir or buttermilk if you like. I do not recommend sour cream or creme fraiche as they have a much higher fat content.