Cut each herring filet in half medium bite-size pieces. Usually, I cut in a half lengthwise then into pieces. Place in a chosen serving bowl.
Add drained peas, chopped red onion, cubed apple, mayonnaise and śmietana. Give it a good mix and season to taste with pepper.
Place in the fridge tightly covered with foil and let it cool for a few hours before serving. Highly recommend a piece of fresh bread with butter on the side.