Wash the vegetables carefully and dry. With a paring knife, cut the caps off the tomatoes, peppers, and eggplant, and both ends off the zucchini and set aside. With a spoon, scoop out the pulp and seeds from the eggplant, zucchini, and peppers, and discard.
Scoop out the tomato pulp, chop well, and set aside. Lightly salt the interior of all vegetables.
Tip: Scoop out vegetables leaving a thin shell, about 1/8 inch.
In a pot, heat 1/2 cup of olive oil and sauté the onion for about 2-3 minutes. Add grated zucchini, eggplant, and carrots, and cook over low heat for 10 minutes. Add the tomato pulp and continue to cook for 5 minutes. Remove from the heat and set aside to cool for 15 minutes, and put in a bowl. Add the rice, parsley, salt, and pepper, and mix well with a spoon until blended.
With a spoon, fill vegetables loosely with the rice mixture, place in a roasting pan packed closely but not squashed, with caps covering the tops and ends. Place tomatoes (and small bell peppers if used) upright, lie the others on their sides. Pour 1/2 cup olive oil and 1/2 cup water over the top, sprinkle the tops of the upright vegetables with toasted breadcrumbs, and bake at 450F (230C) for 1 hour. Halfway through, turn the vegetables that are placed on their sides.