Cook Eggplant: Heat half the oil in a large pan. Fry eggplant cubes until golden and soft (approx. 10 mins). Remove and set aside.
Sauté Aromatics: In the same pan, add remaining oil. Sauté onion, celery, and bell pepper until soft (8 mins). Add garlic and cook for 1 min.
Create Sauce: Stir in tomato paste for 2 mins. Add crushed tomatoes, vinegar, sugar, olives, and capers. Simmer for 10 mins.
Combine: Fold the eggplant back into the sauce. Simmer for 5 mins to blend flavors.
Finish: Stir in basil. Season with salt and pepper. Serve at room temperature for the best flavor.