Cut the eggplants and peppers into small dice.
Brown them in 3 tablespoons of oil for 15 minutes.
In another pan, heat the rest of the oil. Throw in the chopped onions. When they are golden, add the peeled, seeded and crushed tomatoes. Simmer for 10 minutes then stir in the capers, pitted olives and finely chopped celery stalk. Mix well then add the aubergines and peppers.
Moisten with vinegar and water. Salt, pepper and sugar.
Let simmer uncovered for 15 minutes for the vinegar to evaporate and the mixture to thicken slightly.