Wash potatoes, leave skin on and cut in bite-size chunks. Place in pot and cover with water. Bring to a boil, lower to simmer and cook uncovered until potatoes are tender, about 20 minutes. Drain in colander and sprinkle lightly with cold water.
In the meantime, put the rest of the ingredients in a large mixing bowl. Drain potatoes well and add to the bowl.
Mix well and refrigerate until ready to use. Garnish with fresh lettuce and sliced tomatoes.
Yields 4 servings.