Add the ground beef, breadcrumbs, egg, minced onion, Worcestershire sauce, ketchup, Dijon mustard, garlic powder, onion powder, smoked paprika, salt, and black pepper to a large bowl.
Mix gently with your hands or a fork until everything is just combined. Avoid overmixing, as this can make the patties dense.
Divide the mixture into four equal portions. Shape each portion into an oval patty approximately ¾-inch thick.
Make a shallow indentation in the center of each patty with your thumb. This helps the patties maintain their shape while cooking.
Place the patties in the hot skillet and cook for about 3–4 minutes per side, or until nicely browned. They do not need to be fully cooked at this stage.
Reduce the heat to medium and add the butter to the same skillet.Add the sliced onions and mushrooms. Cook for approximately 6–8 minutes, stirring occasionally, until the mushrooms release their moisture and begin to brown. Sprinkle the flour over the mushroom and onion mixture. Stir continuously for about 1 minute to cook the flour.
Add Worcestershire sauce, Dijon mustard, ketchup, thyme, and black pepper. Stir well and bring the gravy to a gentle simmer.
Cover the skillet partially and simmer over medium-low heat for approximately 10–12 minutes, turning the patties once halfway through cooking.
Sprinkle with fresh parsley and serve immediately with creamy mashed potatoes, egg noodles, rice, green beans, broccoli, or your favorite vegetables.