Step 1Place eggplant, onion and tomatoes in large bowl. Toss with 1/2 teaspoon salt and 2 tablespoons oil. Transfer in single layer to shallow roasting pan or jellyroll pan.
Step 2Bake at 400 degrees until eggplant is soft, stirring once, about 30 minutes. Cool on wire rack.
Step 3Transfer vegetables to food processor bowl and add remaining salt, oil, 1 tablespoon water, lemon juice, cilantro and garlic. Process until very smooth, about 1 minute. Add more water if mixture is too thick (it thickens slightly in refrigerator). Stir in capers. Refrigerate at least overnight and up to 5 days.
Step 4To serve, stir well and let come to room temperature. Add more water if mixture is too thick, taste and, if needed, adjust seasoning. Serve at room temperature in small bowl with basket of toasted pita crisps beside it.