1-In a large bowl, combine the ground beef, breadcrumbs, beaten egg, ketchup, Dijon mustard, dried oregano, and salt until well mixed.

2-Form the mixture into four equal oval-shaped patties, each about 3/4-inch thick.

3-Heat the olive oil in a large nonstick skillet over medium-high heat. Add the patties and cook for approximately 3 minutes on each side until a golden crust forms. Remove patties and place them on a plate.

4-Reduce the heat to medium and add the butter to the same skillet with the drippings. Once melted, whisk in the flour until smooth and lump-free.

5-Lower the heat to medium-low and gradually whisk in the beef stock, ketchup, Worcestershire sauce, and onion powder.

6-Add the sliced mushrooms and simmer the gravy for about 5 minutes until it thickens. Season with salt and pepper.

7-Return the patties to the skillet, nestle them into the gravy, cover, and cook for an additional 10 minutes until the internal temperature reaches 160°F (71°C).

8-Serve the Salisbury steaks with the mushroom gravy spooned on top over mashed potatoes, accompanied by optional vegetables or rice pilaf.