In a large saucepan, heat 2 tablespoons olive oil over medium heat. Add the onion and garlic and cook, stirring occasionally, until soft, about 5 minutes. Stir in the eggplant, zucchini and 1 cup water, season with salt and pepper and cook, stirring frequently, for 5 minutes. Add the tomatoes and their juice and bring to a boil. Lower the heat, partially cover and simmer, stirring often, until the vegetables are tender, about 15 minutes. Stir in the basil.