Boil the potatoes with their skin if you wish to eat the skin or without if not.
Mince the onions and the scallions. 
Mince the herbs.
Prepare a vinaigrette with mustard, oil, vinegar and shallot.
When the potatoes are ready cut them in pieces and mix with the onions and scalliosn.
Add the herbs and mix.
Pour the vinaigrette and mix.