Combine ground beef, breadcrumbs, egg, Dijon mustard, 1 tablespoon ketchup, onion powder, garlic powder, salt, and pepper in a mixing bowl. Mix until just combined.
Divide the mixture into 4 equal parts and shape each into an oval patty. Press them slightly to make them about 3/4-inch thick.
Heat olive oil in a skillet over medium-high heat. Add patties and cook for about 4 minutes on each side until browned. Remove and set aside.
In the same skillet, add butter and onions. Cook until onions are soft. Add mushrooms and cook until browned. Sprinkle flour over the mixture and stir to combine.
Gradually add beef broth, stirring continuously. Stir in Worcestershire and ketchup. Bring to a simmer and allow to thicken. Add salt and pepper to taste and adjust other seasonings as needed.
Return the patties to the skillet, nestling them into the gravy. Cover and simmer for 10-15 minutes or until patties are cooked through.
Sprinkle with parsley and serve with mashed potatoes if desired.