Instructions:
1. Prepare the Salisbury Steaks:

In a large bowl, combine the ground beef, breadcrumbs, milk, chopped onion, egg, garlic powder, onion powder, Worcestershire sauce, salt, and pepper. Mix well until fully combined, but be careful not to overwork the meat.
Divide the mixture into 4 equal portions and shape each into an oval or round patty, about 1/2-inch thick.
Heat olive oil in a large skillet or frying pan over medium heat. Once hot, add the patties and cook for 4-5 minutes per side, or until they are browned and cooked through (internal temperature should be 160°F). Remove the patties from the skillet and set aside on a plate.
2. Make the Mushroom Gravy:

In the same skillet, melt the butter over medium heat. Add the chopped onion and cook, stirring occasionally, for about 3-4 minutes until softened.
Add the sliced mushrooms and cook for 5-7 minutes, stirring occasionally, until the mushrooms are browned and tender.
Add the minced garlic and cook for an additional 1 minute, until fragrant.
Sprinkle the flour over the mushroom mixture and stir to coat the vegetables. Cook for 1-2 minutes to eliminate the raw flour taste.
Slowly add the beef broth while stirring constantly, making sure the flour mixture dissolves and the sauce thickens.
Stir in the Worcestershire sauce, soy sauce (if using), thyme, and salt and pepper to taste. Bring the gravy to a simmer and let it cook for 3-5 minutes, until it has thickened to your desired consistency.