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

Shape the mixture into 8 patties (rissoles) about 1/2 inch thick.

Heat olive oil in a large skillet over medium heat. Cook the rissoles for about 5 minutes on each side, or until browned and cooked through. Remove from the skillet and set aside.

In the same skillet, melt the butter over medium heat. Add the sliced mushrooms and cook until they are browned and tender, about 5 minutes.

Sprinkle the flour over the mushrooms and stir to combine. Gradually add the beef broth and soy sauce, stirring constantly until the gravy thickens, about 3-4 minutes.

Stir in the thyme and season with salt and pepper to taste.

Return the rissoles to the skillet, spoon the mushroom gravy over them, and simmer for an additional 5 minutes.

Serve hot with mashed potatoes or rice.