In a large bowl, combine ground beef, breadcrumbs, chopped onion, egg, Worcestershire sauce, garlic powder, salt, and black pepper. Mix until well combined and form into 4 oval patties.

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

In the same skillet, add sliced mushrooms and sauté until they are golden brown, about 5 minutes. Pour in the beef broth and bring to a simmer.

In a small bowl, mix cornstarch and water to create a slurry. Stir the slurry into the mushroom gravy and add soy sauce and thyme. Cook for an additional 2-3 minutes until the gravy thickens.

Return the patties to the skillet, spoon the mushroom gravy over them, and simmer for another 5 minutes to heat through.

Serve warm, ideally with mashed potatoes or rice.