Hard boil the egg in boiling water for about 10 minutes, drain, quench and peel. Dice the cucumber. Wash apple, quarter it, cut out core. Cut quarter into pieces.
Remove the skin from the sausage. Cut the sausage into strips. Cut herrings into pieces. Peel and grate onion. Mix oil, mustard, vinegar and onion. Season with salt and pepper. Wash parsley, shake dry and chop finely.
Fold capers and parsley into the marinade. Mix cucumber, apple, sausage and herring pieces with marinade. Cut bacon into small cubes in a pan without fat and add to the herring salad.
Arrange on plates. Cut the egg into slices and add to the salad. Garnish with caper apples. Serve with brown bread.