To prepare the caponata conventionally, preheat oven to 325°F. Meanwhile, in an oven-going Dutch oven, heat 2 tablespoons oil over medium heat. Add celery and onion; cook, covered, for 10 minutes, stirring occasionally. Stir in tomatoes, eggplant, zucchini, parsley, raisins, tomato paste, vinegar, brown sugar, salt, and pepper. Bake, covered, about 2 hours or until vegetables are tender. If desired, stir in olives and/or capers.