Peel the eggs and cut in half and remove the yolks. Chop the whites.
Push the egg yolk through a fine mesh sieve, then mix to a smooth paste together with the mayonnaise, mustard, vinegar and soured cream. Season to taste with salt and pepper.
Mix the dressing with the tomatoes, pepper, potatoes, egg white and spring onions.
Carefully split the pittas in half to form pockets. Fill the pockets with the salad.