Preheat oven to 350 degrees. Line half sheet pan with heavy-duty foil, spray lightly with nonstick cooking spray and set aside.
In a large skillet, 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, pepper, seasonings, 1 cup ketchup, Worcestershire sauce and parsley. Mix well until completely combined.
Form into a long log on the prepared baking sheet and flatten the top.
In a small bowl, whisk brown sugar with remaining 1 1/2 cups 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 degrees F. Rest meatloaf covered lightly with foil for 10-15 minutes before cutting. Top with more chopped parsley, if desired, and serve.