Cut the eggplant into chunks. In a colander, toss the eggplant with 1 tsp. salt, then let drain for about 30 minutes. Pat the eggplant dry with paper towels.
Meanwhile, spray a deep 9 x 13-inch baking dish with cooking spray. Set aside. Preheat oven to 400 degrees F.
In a large bowl (or in the prepared dish), toss together eggplant, onion, bell peppers, zucchini, tomatoes, parsley, basil, oregano, tomato paste, olive oil, and garlic.
Transfer vegetables to the prepared dish, cover with foil, and bake for 45 minutes, stirring once or twice during the baking time to make sure that the vegetables cook evenly (or until vegetables are tender). Garnish with capers, drizzle with olive oil, and season with salt and pepper just before serving.