In a Dutch oven or large (5-quart) saucepan with a lid, heat 6 tablespoons oil over medium-high. Add eggplant; cook, stirring occasionally, until softened, 6 to 8 minutes. Transfer to a bowl; set aside.
Add remaining 2 tablespoons oil to pan; reduce heat to medium. Add onion, bell pepper, zucchini, and garlic. Season with salt and pepper; cook, stirring occasionally, until vegetables have softened, 7 to 10 minutes.
Add beef; cook, stirring and breaking up meat with a spoon, until no longer pink, 5 minutes.
Bring a large pot of salted water to a boil. Meanwhile, add tomatoes, oregano, and eggplant to beef-vegetable mixture; season with salt and pepper. Bring to a boil; reduce heat to medium-low. Simmer, stirring occasionally, until sauce is thick and eggplant is tender, about 25 minutes. Season with salt and pepper.
Meanwhile, cook pasta until al dente, according to package instructions. Drain; serve topped with sauce and, if desired, Parmesan.