Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the ground beef, chopped onion, garlic, and zucchini.
Add the egg, Worcestershire sauce, oregano, salt, pepper, parsley, and parmesan cheese if using. Mix until just combined.
Shape the mixture into a loaf and place it in a greased baking dish.
Bake in the preheated oven for about 45-55 minutes, or until the internal temperature reaches 160°F (70°C).
Remove it from the oven and let it rest for about 10 minutes before slicing.
Slice and serve with your favorite side dishes.