To make the dressing just whisk all the ingredients for the master dressing together. Other things will get added to this base as we season each item.

For the roasted peppers, quarter and core the pepper then put it right under a broiler with the skin side up, until it is completely charred on that side (it's okay if there's a little red still showing). Transfer the peppers into a plastic bag and seal it. The steam helps loosen the skins and when the peppers have cooled, you should be able to remove the skin with no difficulty. Once you've peeled them, put them back in the bag and drizzle enough olive oil on them to coat, then toss them with the oregano salt and pepper. This can be made in advance

For the potatoes, boil them in well salted water until you can just barely pass a fork through them (they should still be a little firm). Remove them from the water and allow them to cool enough to handle. Slice them into cubes then toss them with 3 Tbs of dressing and parsley. Add salt and pepper as needed and set aside. This can be made in advance

For the haricots vert, return the potato water to a boil and add more salt (it should taste like the ocean). Prepare an ice bath by filling a bowl with water and ice cubes. Add the haricots vert and boil until they're bright green and tender, but they still have a bit of crunch (a minute or two, longer if you're using older beans). Drain and put them into the ice bath to "shock" them, this should make them turn a very vibrant green color. You don't want to dress these too early since the vinegar will make them discolor. If you're doing this in advance, wrap them and refrigerate until you're ready to serve them.

For the tomatoes, toss them with the onions and capers along with a little olive oil, salt and pepper.