Using a cuttng board, finely chop a medium sized onion.
In a large mixing bowl, combine,, ground beef, onion, panko crumbs, egg, salt, garlic salt, ground black pepper and, mustard.
Mix well until all ingredients are thoroughly combined.
Form into 6 round or oval shaped patties.
In a large skillet, brown the patties on both sides.
When cooked through, remove the patties from the skillet and set aside on a plate.
Leave all the bits from the patties int the pan.
Add all of the sauce/gravy ingredients to the pan and stir.
Bring the gravy to a boil and then reduce heat.
Carefully lift patties and place into the gravy.
Spoon gravy over the patties and reheat.
Serve when re-heated.