Toss eggplant, red pepper, onion, and tomatoeswith half of olive oil, rubbing them with your hands to coat them evenly. Season with salt and pepper. Wrap each vegetable individually in foil. Preheat oven to 350°F. Place foil packets on a rimmed baking sheet and bake until vegetables are completely tender, about 2 hours. Unwrap vegetables and discard eggplant, pepper, onion, and tomato skins. Discard pepper and eggplant seeds. Roughly chop flesh and combine with remaining olive oil and parsley. Season to taste with salt and pepper. Serve, drizzling with sherry vinegar.