Cut the onion into half rings and marinate for 20 minutes in cold water (100 ml) with the addition of apple cider vinegar and sugar. Meanwhile, peel the eggplants and cut them into half slices. Fry in vegetable oil until tender. Place the eggplants on paper towels to remove excess oil.
Put diced tomatoes and eggs in a salad bowl. Squeeze the onion and add to the salad along with the chilled eggplant. Add salt, ground pepper and, if necessary, olive oil. Stir the salad.