peel the tomatoes and coarsely chop. Peel the eggplant and cut into ½-inch dice. Peel and finely chop the onion.
Put the onion and 3tablespoons of the olive oil in a 10-inch skillet and place over medium-high heat. Sauté, stirring occasionally, until the onion turns a rich golden color, about 5 minutes.
While the onion is sautéing, peel and finely chop the garlic. Finely chop enough of the parsley leaves to measure 2tablespoons. When the onion is done, add the garlic and parsley, stir for about 1 minute, then add the tomatoes and eggplant. Season with salt and pepper and cook until the tomatoes are no longer watery and the eggplant is tender, 15 to 20 minutes.
While the eggplant and tomatoes are cooking, peel the shrimp, devein, and cut into ½-inch pieces.
Fill a pot for the pasta with at least 6quarts water, place over high heat, and bring to a boil. When the eggplant and tomatoes are done, add about 2tablespoons salt to the boiling water, put in the spaghetti, and stir until all the strands are submerged. Cook until al dente.
While the pasta is cooking, add the shrimp to the sauce, season with salt and pepper, and cook until they are pink, 2 to 3 minutes. Remove from the heat.
Drain the pasta, toss it with the sauce and the remaining 1tablespoon olive oil, and serve at once.
You can make the sauce through step 3 up to 1 day ahead of time. Store, covered, in the refrigerator. Reheat the sauce before proceeding.