Trim off the ends of the eggplant and zucchini.  Do not peel.  Cut each into cubes measuring about 1 inch or slightly larger.  There should be about 9 cups of eggplant cubes and 6 of the zucchini.
Peel the onions and cut into ½ inch cubes.  There should be about 1 ½ cups.
Core, seed, and devein the green peppers, and cut them into 1 inch pieces.  There should be about 2 ½ cups.
Heat the oil in a large heavy casserole and add the eggplant and zucchini.  Sprinkle with salt and pepper.  Cook, stirring often, over high heat until the vegetables start to brown, about five minutes.
Add the onions, green peppers and garlic.  Cook, stirring, over high heat, about two minutes.  Add the tomatoes and tomato paste, and stir to blend.  Add the bay leaf, thyme and capers.  Add salt and pepper.  Bring to the boil and cover.  Reduce the heat and let simmer 30 minutes.  Stir in the parsley and remove from the heat.