In a large bowl, mix together ground beef, breadcrumbs, chopped onion, egg, ketchup, Worcestershire sauce, garlic powder, salt, and pepper.

Form the mixture into 4 oval patties.

Heat olive oil in a large skillet over medium heat. Add patties and cook until browned on both sides. Remove patties and set aside.

In the same skillet, add butter, mushrooms, and sliced onion. Cook until softened.

Sprinkle flour over the vegetables and cook for 1 minute, stirring constantly.

Gradually whisk in beef broth, and bring the mixture to a simmer. Cook until the gravy has thickened.

Return the patties to the skillet, spooning gravy over them. Cover and simmer for 10 minutes, or until the beef is cooked through.