In a large mixing bowl, combine the ground beef, breadcrumbs, grated Parmesan, egg, garlic powder, salt, and pepper. Mix gently until just combined to avoid tough patties. Shape into 4-6 oval patties, about 1 inch thick.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add the patties and sear for 3-4 minutes on each side until browned and crispy. Remove and set aside.

In the same skillet, add remaining olive oil and sauté sliced mushrooms and onions over medium heat for about 5 minutes until tender.

Slowly pour in beef broth, scraping the bottom of the skillet. Stir in Worcestershire sauce. For thicker gravy, add a slurry of flour and water, then whisk it in. Simmer for 5-7 minutes until thick.

Return the patties to the skillet, cover, and reduce to low heat. Simmer for 10 minutes, letting the patties absorb the flavors.

Plate the Salisbury steak with gravy and serve with mashed potatoes and steamed vegetables.