Preheat the oven to 350°F (175°C).
In a medium skillet, heat a little oil over medium heat. Sauté the diced onion, garlic, bell pepper, zucchini, and carrot until softened, about 5-7 minutes. Remove from heat and let cool slightly.
In a large mixing bowl, combine the ground beef, breadcrumbs, Parmesan cheese, cooked vegetables, eggs, milk, Worcestershire sauce, oregano, salt, and black pepper. Mix well until all ingredients are thoroughly combined.
Transfer the meat mixture into the 9x13 inch baking dish, shaping it into a loaf shape.
Pour the marinara sauce evenly over the top of the meatloaf.
Sprinkle the shredded cheddar cheese on top of the marinara sauce.
Bake in the preheated oven for 40-45 minutes, or until the internal temperature of the meatloaf reaches 160°F (70°C) and the cheese is bubbly and golden.
Remove from the oven and let rest for 10 minutes before slicing and serving.