Finely chop the onion. Marinate in vinegar, sugar, and add a few tablespoons of water.
Cut the herring into small cubes. Grate the vegetables on a medium grater.
Place the chopped herring, grated vegetables, and onion in a bowl. Set aside one beet for garnish. Add mayonnaise to the salad and mix.
Place the resulting mixture on a plate. The salad can be any shape. Grate the remaining beetroot on top and spread it over the entire surface. Cover with mayonnaise. You can decorate with anything: eggs, tomatoes, cucumbers, herbs, olives.