Borscht, when I was growing up, was always served with sour cream to mix in as you desired, and with diced cucumbers to drop in for a fresh crunch in the soup. So I thought, "Why not combine these ingredients into a salad?" Thus, the borscht salad was born.
Beets, cooked, peeled, and cubed
Cucumbers, peeled, seeded and cubed
salt and pepper, to taste
The ratio of beets to cucumber is up to you. Since the cukes were the garnish to the soup, I like to use about 3/4 beets and 1/4 cucumber. Add as much sour cream as you like, and season to taste. You could go wild ad add some chopped onion, but I don't think it's necessary.
And if you aren't fond of cucumbers, you can use zucchini as well. Once the sour cream is mixed in and it turns a vivid pink, it doesn't matter much, except that the zuccini absorb the beet color faster than the cucumbers do.