Look for firm eggplant with a smooth skin and a uniform color. They should be heavy for their size and the flesh should bounce back when pressed with fingers. Usually, smaller eggplants are sweeter and more tender than larger ones.
Cut eggplant into 1 inch cubes. Thinly slice onions. Cut celery into 1 inch pieces. Cut olives crosswise in half.Heat the wok over medium high heat until hot. Drizzle 1 tablespoon of oil into the wok and heat 30 seconds. Add onions and celery and stir fry about 2 minutes or until tender. Move onions and celery up the side of the wok. Reduce heat to medium.Add remaining 1 tablespoon oil and eggplant to the wok. Stir fry eggplant about 4 minutes or until tender. Add tomatoes and mix well. Cover the wok and cook 10 minutes.Stir olives, sugar, caper, vinegar, and oregano into eggplant mixture. Season with salt and pepper to taste.Transfer to serving platter.Garnish, if desired.