For dressing: mix the extra-virgin olive oil, balsamic vinegar, fresh lemon juice, salt and pepper to taste. Set the dressing aside.
Wash the potatoes and put them into a pot. Pour water until potatoes are covered and bring to boil. Add a teaspoon salt and reduce heat to medium. Cover the pot and simmer until done - a fork can easily be poked through them. Drain water from potatoes, peel and slice them.
In a bowl combine the sliced potatoes, beets, grape tomatoes and black ripe olives. Sprinkle dressing over salad. Garnish with the feta cheese and serve.