For the meatloaf: Preheat the oven to 400 degrees F. Coat a half-sheet pan with cooking spray and sprinkle with the breadcrumbs, which will absorb the juices during cooking.
Pour the milk over the bread in a bowl and allow it to soak up the milk. Place the ground beef, milk-soaked bread, Parmesan, seasoned salt, parsley and pepper in a large mixing bowl. Pour in the eggs. With clean hands, mix the ingredients until well combined.
Pat the mixture evenly into the prepared sheet pan, spreading all the way to the edges and corners.
Next, make the glaze: Whisk together the ketchup, brown sugar, balsamic vinegar and Worcestershire sauce in a bowl until well combined. Brush the mixture evenly over the top of the meatloaf. Sprinkle with the bacon.
Bake until the meat is cooked through and slightly browned, 20 to 25 minutes.
Remove from the oven, then cut into squares and serve with the mashed potatoes. Garnish with the chopped parsley.