Rinse the fillet with cold running water. Pour water over the fillet so that the water completely covers the meat. Cook the chicken over moderate heat without a lid and remove the foam if necessary. After the water boils, cook the chicken fillet for another 15 minutes, then leave the chicken to cool. Cut the finished chicken fillet into large squares.
Cut the apples into strips and the onion into half rings.
Mix mayonnaise and mustard.
Place the ingredients in a deep bowl, add salt and ground black pepper to taste. Mix the salad ingredients thoroughly.
Place the salad on serving plates.