Cut the onion into half rings and marinate for 20 minutes in cold water (100 ml) with Apple cider vinegar and sugar. Meanwhile, peel the eggplant and cut it into half slices. Fry in vegetable oil until tender. Put the eggplant on paper towels to remove excess oil.
In a salad bowl, put the diced tomato, as well as the eggs. Squeeze the onion and add to the salad along with the cooled eggplant. Add salt, ground pepper and if necessary olive oil. Mix the salad.