Place the potatoes unpeeled in a large pot, add enough water to cover them well. Bring the water to a boil. Cooking until the potatoes are tender but not mushy, usually about 20 minutes for medium potatoes.
Remove the cooked potatoes from the water with a skimmer and place in a colander to cool.
Now add the green beans to the same pot along with a good pinch of salt. Boil them until they are crisp-tender. This can take anywhere from 5 to 15 minutes depending on the bean. Remove them to another colander and rinse them with cold water to cool them quickly. Let them drain.
While the vegetables are cooling/draining, you can turn to your vinaigrette. Whisk the oil and vinegar together in a small bowl until they have fully emulsified. Stir in the minced garlic, shallot or scallion, along with the minced herbs and a good pinch of salt and a grind of pepper. Taste and adjust for seasoning, then set aside until needed.
As soon as the potatoes are cool enough to handle but still warm, peel them with a paring knife, then cut them into bite sized pieces and place them in a mixing bowl. Add the green beans. Pour the vinaigrette over the vegetables then toss well, until they are well covered with the vinaigrette.
Give the salad a final taste and adjust for seasoning if need be.
Let the salad rest for at least 30 minutes before serving.