The first step is to cook the potatoes and eggs. For potatoes, to maintain maximum consistency, vitamins, and flavor, you must cook them with the skin. In a medium saucepan, add potatoes and enough water to cover potatoes by 1 inch. Add 1/2 teaspoon of salt. Bring to a boil and continue on a low boil until potatoes are just beginning to get soft. Remove from heat and let cool. Peel potatoes once they are cool enough. Quarter potatoes.
To hard boil the eggs: In a medium saucepan, add eggs and ½ teaspoon salt and cover with cool water (water should be about 1 inch above the eggs). Bring to a strong rolling boil and let boil for about 30 seconds. Then turn heat off and let sit for about 12 minutes. Drain hot water and cover eggs with cool water to stop cooking. When cooled, peel the eggs. ****Quarter eggs, but save 1 cooked egg yolk for dressing.
Prepare vegetables (slice tomatoes into wedges, pepper into strips and onion into thin slices) as eggs and potatoes are cooking and add to a bowl.
Add potatoes, olives and capers. Add egg and tuna.
To prepare the dressing, crush the cooked yolk that you reserved, mix very well with oil and vinegar until you have a homogenous dressing. Salt and pepper dressing, to taste. Top salad with dressing.