Always sweat the onions and garlic; you'll rarely need to add more salt later on. The eggplant can be peeled if desired. It can also be baked in advance and refrigerated or even kept frozen (if there's a glut) until required. Any pasta can be used in this dish; in the past I've made it with shells, rigatoni and bowtie. The water is used as needed purely as a thinner if the mixture gets too sticky during cooking.