How to Make It
Put the potatoes in a medium pot of salted water. Bring to a boil. Boil until the potato slices are barely tender, about 5 minutes. Drain the potatoes thoroughly.
Meanwhile, heat the broiler. Stand the whole bell pepper upright and cut the flesh from each of the sides, leaving the stem, seeds, and core behind. Put the pepper and the plum-tomato halves on an aluminum-foil-lined baking sheet, cut-side down. Broil until charred, about 5 minutes. Peel off and discard the blackened skin.
Put the roasted pepper and tomatoes in a food processor or blender. Add the almonds, garlic, paprika, cayenne, vinegar, oil, 3/4 teaspoon of the salt, and the black pepper. Puree until almost smooth.
In a large glass or stainless-steel bowl, toss the sardines with the potatoes, the bell-pepper strips, and the remaining 1/4 teaspoon salt. Toss the salad with 1 cup of the romesco sauce and sprinkle the parsley over the top. Pass the remaining romesco sauce at the table.