Preheat the oven to 350°F. In a large mixing bowl, combine the ground beef, zucchini, eggs, bread crumbs, onion powder, garlic powder, Italian seasoning, salt, and pepper.
Mix with a sturdy spoon or your hands until well combined. Divide the mixture into two parts on a large baking sheet and use your hands to shape it into meatloaf forms.
In a small bowl or measuring cup, whisk together the ketchup, balsamic, and brown sugar. Generously pour and brush the mixture over both meatloaves.
Bake for 60-70 minutes, until the internal temperature of the center of the meatloaf reaches 160°F. Let rest for 10 minutes before slicing.
Notes
This recipe can be divided in half if smaller amounts are desired. When reducing the recipe, simply use 2 eggs, instead of trying to measure half of one egg.The cooking time will be shorter for a single meatloaf in the oven. Check for doneness every 5-10 minutes, starting at 50 minutes. I always make this full recipe, as the leftovers will keep nicely for several days. (That is, if we're lucky enough to have leftovers with three teenagers in the house.)