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

Shape the mixture into 4 oval patties.

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 beef broth and soy sauce, scraping up any browned bits from the bottom.

In a small bowl, mix cornstarch and water to create a slurry. Stir the slurry into the broth mixture and cook until the gravy thickens, about 2-3 minutes.

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

Serve the Salisbury steaks with the gravy over mashed potatoes or rice.