Preheat oven to 350 degrees Fahrenheit.

In a large bowl, add the beef, flaxseed meal, onion, milk, egg, ketchup, Worcestershire sauce, parsley, salt, garlic powder, and pepper. Use your hands to mush and mix these ingredients together until well combined.

Add the meat mixture to a loaf pan. Pat the meat down into an even layer.

In a small bowl, add 1/4 cup ketchup, the brown sugar, and vinegar. Stir to combine. Pour the sauce on top of the meatloaf and spread into an even layer.

Bake uncovered for 55 minutes.

Let the meatloaf rest for 8-10 minutes before serving.