Coat 2 cookie sheets with 2 tablespoons olive oil each, spread with eggplant and roast about 10-12 minutes. Remove.
Saute garlic in 2 tablespoons olive oil over moderate heat until fragrant, about 15 seconds. Add the onions and celery and cook, stirring, until lightly browned, about 10 minutes. Add the tomatoes, cover and cook over moderately low heat, stirring occasionally, about 10 minutes.
Stir together vinegar and sugar. Add to the onion-tomato mixture along with the eggplant and raisins. Cover and cook over moderately low heat, stirring occasionally, until all the vegetables are tender, about 20 minutes. (May be made to this point up to 3 days ahead. Cover and refrigerate.).
When ready to serve, let come to room temperature and stir in remaining ingredients. Serve with pita bread crisps.