For this recipe it is not necessary to peel the tomatoes. Wash them under cold running water and dry with paper toweling. Cut off a thin slice at the base. Pare into and around the stem and discard the core. Slice the tomatoes onto a round serving dish, arranging the slices neatly. Sprinkle the slices with salt. The important thing to know is that raw tomatoes, more than any other vegetable, take well to a more than customary amount of salt. They also take well, oddly enough, to a large amount of vinegar.
When the tomatoes are sprinkled with salt, add the pepper. Scatter the onions over the slices, then sprinkle with the parsley, vinegar, and oil. This dish is especially good with a crusty loaf of French bread.