Place the peas in a microwaveable bowl and cook on full power to either defrost the frozen peas or too just cook the fresh peas. Set aside.
Wash the potatoes if they are dirty (do not peel them), place in a pan with enough cold water to cover them. Bring to the boil and cook for 20 or until a knife goes into them with ease.
While the potatoes are cooking you can mix the mustard and mayonnaise together in the bowl you will serve the potato salad from.
Chop the fresh parsley into smallish bits and the green onions into slices. Mix into the mayo/mustard mixture and add the pepper and peas.
After you make sure the potatoes are cooked. Drain the water from the pan and dry them a little on the turned off cooking ring.
Place the potatoes in the bowl that has the mayo/mustard in it. Turning the potatoes over in the mixture and coat the potatoes well. If you find the mustard/mayo is too thick, you can add some or all of the tbsp of milk.
Chill the salad if you like yours chilled. I prefer it warm or at room temperature. Only keep at room temperature if you are just about to eat, other wise put in the fridge to chill.
Note: You could add more mayo if you want. I was making this for my sparkpeople lifestyle diet.