Prepare the Meatball Mixture: In a large bowl, combine ground beef, breadcrumbs, egg, ketchup, mustard, Worcestershire sauce, seasoning salt, pepper, and onion powder. Mix until just combined; avoid overmixing.

Shape the Meatballs: Roll the mixture into evenly sized meatballs (about 1½ inches in diameter). You should get around 18-20 meatballs.

Cook the Meatballs: Heat olive oil in a large skillet over medium heat. Add the meatballs in batches, browning them on all sides. Transfer the browned meatballs to a plate and set aside (they don’t need to be fully cooked yet).

Sauté the Onions: In the same skillet, melt the butter over medium heat. Add the chopped onions and cook for 5-7 minutes, stirring occasionally, until softened and golden brown.

Make the Gravy Base: Sprinkle the flour (or cornstarch) over the onions and cook for 1-2 minutes, stirring constantly to avoid lumps. Gradually whisk in the beef broth, Worcestershire sauce, seasoning salt, and ketchup. Simmer until the gravy thickens (about 3-5 minutes).

Combine Meatballs and Gravy: Return the meatballs to the skillet, ensuring they’re coated in the gravy. Cover and simmer for 10-15 minutes, or until the meatballs are fully cooked and tender.

Garnish and Serve: Sprinkle freshly chopped parsley over the meatballs. Serve hot with mashed potatoes, rice, or crusty bread to soak up the rich gravy.