In a mixing bowl, combine ground beef, bread crumbs, egg, Worcestershire sauce, garlic powder, onion powder, salt, and pepper. Mix until just combined.

Form the mixture into 4 oval patties.

Heat a skillet over medium heat and add a little oil. Cook the patties for about 4-5 minutes on each side until browned and cooked through. Remove from skillet and set aside.

In the same skillet, melt butter over medium heat. Add sliced mushrooms and chopped onion, cooking until softened, about 5 minutes.

Sprinkle flour over the mushrooms and onions, stirring to combine. Cook for 1 minute.

Gradually whisk in beef broth and soy sauce, bringing to a simmer. Cook until thickened, about 5-7 minutes.

Stir in heavy cream if using, and return the patties to the skillet, spooning gravy over them.

Serve the Salisbury steaks hot, garnished with additional parsley if desired, alongside mashed potatoes or rice.