In a mixing bowl, combine the ground beef, breadcrumbs, chopped onion, milk, egg, garlic powder, Worcestershire sauce, salt, and pepper. Mix until well combined, but do not overwork the meat.
Form the mixture into meatballs, about 1 inch in diameter.
In a skillet over medium heat, brown the meatballs on all sides for about 5-7 minutes. This step adds extra flavor but can be skipped if desired.
Place the meatballs in the slow cooker.
In a separate bowl, mix the cream of mushroom soup, beef broth, soy sauce, ketchup, and dried parsley. Pour the gravy mixture over the meatballs in the slow cooker.
Cover and cook on low for 6 hours or until the meatballs are cooked through and tender.
Once done, gently stir the meatballs in the gravy before serving.