Preheat oven to 450°F. In a large skillet, heat olive oil over medium heat. Add onion and cook until tender, 6 to 8 minutes. Add the mushrooms and garlic. Cook 2 minutes more.
Add the tomatoes and eggplant and season with the salt and pepper. Cook, stirring occasionally, until the vegetables are tender and tomatoes begin to break down, 10 minutes.
Meanwhile, bring a large pot of lightly salted water to a boil. Add the macaroni and boil for 6 minutes; drain. Add the pasta, herbs, and 1/4 cup of the Parmesan cheese to the vegetable mixture. Stir to combine. Transfer the vegetable mixture to a 3-quart baking dish. Sprinkle with remaining 1/2 cup Parmesan cheese.
Bake for about 5 minutes or until the cheese is golden brown.
The list of ingredients doesn't mention onion. How much chopped onion should I use ????