Step 1: Prepare the Hamburger Steaks

1. In a large bowl, combine the ground beef, breadcrumbs, egg, Worcestershire sauce, garlic powder, onion powder, salt, and pepper. Mix until just combined; do not overwork the meat.
2. Divide the mixture into 4 equal portions and shape each into a patty.

Step 2: Cook the Hamburger Steaks

1. Heat a large skillet over medium-high heat and add a small drizzle of olive oil.
2. Place the hamburger steaks in the skillet and cook for 4-5 minutes on each side, until browned and cooked through. Remove the patties from the skillet and set them aside.

Step 3: Make the Mushroom Onion Gravy

1. In the same skillet, add another tablespoon of olive oil, if needed. Add the sliced onions and mushrooms and cook for 5-7 minutes until softened and lightly browned.
2. Add the minced garlic and cook for 1 minute, until fragrant.
3. Stir in the beef broth and Worcestershire sauce, scraping up any browned bits from the bottom of the pan.
4. In a small bowl, mix the cornstarch with water to create a slurry. Slowly whisk it into the gravy to thicken, stirring until the gravy reaches your desired consistency.
5. Season the gravy with salt and pepper to taste.

Step 4: Combine and Serve

1. Return the hamburger steaks to the skillet, spooning the mushroom onion gravy over the top.
2. Let simmer for a few minutes to heat through.
3. Garnish with fresh parsley, if desired, and serve hot with mashed potatoes, rice, or noodles.