Preheat your oven to 350°F (175°C) and line a rimmed baking sheet with parchment paper or foil.
In a medium skillet over medium heat, heat olive oil and sauté the chopped onion for 5–7 minutes until soft and golden. Let cool slightly.
In a large mixing bowl, combine ground beef, sautéed onions, eggs, garlic, ketchup, parsley, breadcrumbs, milk, salt, Italian seasoning, and pepper. Mix gently until just combined.
Shape the meat mixture into a loaf about 8x4x3 inches on the prepared baking sheet. Bake uncovered for 40 minutes.
While baking, mix together ketchup, white vinegar, brown sugar, garlic powder, and onion powder to make the glaze.
After 40 minutes, spread the glaze over the meatloaf and return to the oven for another 20 minutes, or until internal temperature reaches 160°F (71°C).
Let the meatloaf rest for 10–15 minutes before slicing to retain juices.