In a large mixing bowl, combine the ground beef, breadcrumbs, beaten egg, Worcestershire sauce, garlic powder, salt, and pepper. Mix until just combined and form into patties.

Heat a skillet over medium heat and cook the patties until browned and cooked through, about 5-7 minutes on each side. Set aside.

In the same skillet, add the sliced mushrooms and onions. Sauté until softened, around 5 minutes.

Pour in the beef broth and bring it to a simmer.

Return the cooked patties to the skillet, allowing them to soak up the gravy flavors for a few minutes.

Meanwhile, in a pot, boil the potatoes and garlic until tender. Drain and mash them with milk, butter, salt, and pepper until creamy.

Plate the Salisbury steak on the garlic mashed potatoes, finishing with a generous drizzle of the mushroom & onion gravy.