Preheat the oven to 400°F Combine the tomatoes, eggplant, zucchini, onions, garlic, and olive oil in a large roasting pan and roast, stirring occasionally, until the eggplant is tender, about 30 minutes.
Put the mixture into a bowl and add the vinegar, salt, pepper, water, and bread. Refrigerate and allow to cool for several hours or overnight.
Pour the mixture into a food processor or blender. You can put it through a food mill or strainer to remove any remaining solids.