1. Heat two tablespoons oil in a large pot over medium heat. Add onions and one teaspoon salt and stir to combine. Cook for about five minutes, until softened.
2. Add eggplant, zucchini, pepper, garlic, basil, oregano, and mustard. Continue to cook for 15–20 minutes, until vegetables are soft and fragrant.
3. Add remaining two tablespoons oil, one teaspoon salt, and black pepper, followed by the pasta, milk, and water. Cover pot and bring to a boil.
4. Once boiling, reduce heat to low and simmer for about 15 minutes, until liquid has absorbed and pasta is cooked through.
5. Stir in mozzarella cheese until melted. Serve immediately.
To prepare ahead, pasta can be prepared the night before or earlier in the day. For best results, prepare until pasta is cooked, then heat it up and add the cheese just before serving.