Preheat the oven to 400 degrees F (200 degrees C).

Toss zucchini and onions in a large bowl with olive oil until evenly coated. Spread vegetables into a large baking dish.

Roast in the preheated oven until golden, about 30 minutes. Remove from the oven and season with salt and pepper. Reduce the oven temperature to 350 degrees F (175 degrees C).

When the vegetables are almost finished roasting, bring a large pot of lightly salted water to a boil. Add pasta and cook, stirring occasionally, until tender yet firm to the bite, about 11 minutes; drain.

Lightly grease a 9x13-inch baking dish.

Heat marinara sauce in a saucepan over medium heat until hot. Spread hot sauce into the prepared baking dish. Top with cooked pasta, followed by roasted zucchini and onions. Sprinkle with Parmesan cheese.

Bake in the preheated oven until sauce is bubbly, 35 to 40 minutes. Remove from the oven and let rest for a few minutes before serving.