In a large bowl, combine the ground beef, breadcrumbs, chopped onion, egg, Worcestershire sauce, garlic powder, salt, and black pepper. Mix until well combined.

Shape the mixture into 4 oval patties, about 1/2 inch thick.

Heat olive oil in a large skillet over medium heat. Add the patties and cook for about 4-5 minutes on each side, until browned and cooked through. Remove the patties from the skillet and set aside.

In the same skillet, add the sliced mushrooms and cook for about 5 minutes until they are softened. Add the minced garlic and cook for an additional minute.

Pour in the beef broth and soy sauce, stirring to combine. Bring to a simmer.

In a small bowl, mix the cornstarch and water to create a slurry. Slowly add this to the skillet, stirring constantly until the gravy thickens, about 2-3 minutes.

Return the patties to the skillet, spoon the gravy over them, and let them simmer for an additional 2 minutes.

Serve hot, garnished with fresh parsley.