Wash potatoes, carrots and parsley root (do not peel), place in a pot, cover with water, salt and cook covered until soft, for about 40 minutes.
Drain, cool, peel and dice, transfer to a large bowl.
Hard-boil eggs (about 5-6 minutes after water boils), dice and add to the bowl with vegetables.
Peel pickled cucumbers, onion and apple, dice and add to the bowl. Add well-drained and dried peas.
Season with salt (about 1/2 teaspoon) and ground black pepper (about 1/2 teaspoon). Mix with mayonnaise (reserve a few tablespoons for decoration) and mustard.
Transfer to a salad bowl and cover with reserved mayonnaise, decorate as desired.