Peel the beets and use a food processor to shred them.
Put the beets and water in a pot, bring to a boil and simmer for 20 minutes. Add the carrots, lemon zest and onion and simmer for 20 more minutes. Skim off any foam. Remove from heat and add lemon juice, salt and pepper.
You could serve the soup hot, or cold by chilling for a few hours or overnight in the fridge.
When serving, put a tablespoon of sour cream into each bowl and sprinkle with goji berries.