Preheat oven to 350° F. Line half sheet pan with heavy-duty foil, spray lightly with nonstick cooking spray and set aside.
In a large skillet, over medium heat, saute onions in olive oil until tender and browned, about 10 minutes. Pour into a large bowl.
To the onions, add in ground beef, bread crumbs, eggs, milk, salt, black pepper, onion powder, garlic powder, Italian seasoning, half of the ketchup, Worcestershire sauce, and parsley. Mix well just until completely combined. Do not over mix.
Form into a long log on the prepared baking sheet and flatten the top.
In a small bowl, whisk brown sugar with remaining ketchup to form glaze.
Spread glaze overtop prepared meatloaf and bake covered with foil* 45 minutes to 1 hour or until cooked thoroughly and registers at least 160° F.
Rest meatloaf covered lightly with foil for 10-15 minutes before cutting. Top with more chopped parsley, if desired, and serve.