We fry eggplants in vegetable oil on a fire above average, until ready, I used an electric grill, because I wanted characteristic stripes. We put it on a dish (we don't salt it, because we already had eggplants in salted water for half an hour). In a separate frying pan, fry the onion over high heat for 2-3 minutes, add the remaining vegetables and over high heat, with the addition of oil, stirring constantly, bring the vegetables to the state of "al dente", that is, the vegetables are almost ready, but crunchy, add sugar.
At the end, add the tomato slices, as soon as they become a little softer, remove from the heat, add salt.