Cut herring fillets into bite-sized pieces, core the peppers and cut into small cubes. Peel, core and dice the tomatoes. Chop the vegetable onions into slightly larger cubes and cut the pickled cucumbers into fine slices. Wash the parsley thoroughly and chop it finely.
Season all ingredients with about 1 tablespoon of oil, 1-2 tablespoons of vinegar and fresh pepper. You can actually do without salt, as the matjes fillets are salty in themselves.