Mix ground beef with garlic salt, steak seasoning, diced onion, bread crumbs, beaten egg, dried parsley and steak sauce until fully incorporated.
Form meat mixture into 6 oval-shaped patties.
Drizzle olive oil into a non-stick skillet over medium low heat. Add salisbury steaks and lightly brown for about 2 minutes on each side. Continue to cook steaks in skillet until no longer pink in the middle (about 10 minutes).
Remove steaks from skillet and keep warm on a plate covered with aluminum foil.
Drain grease from skillet.
Mushroom Gravy
Melt a tablespoon of butter in the same skillet over medium heat. Add sliced onions and mushrooms. Sauté for 2 minutes.
Add soy sauce and sauté until mushrooms and onions are soft (about 3 more minutes).
Sprinkle mushrooms and onions with dried parsley and black pepper.
Pour beef broth into skillet and bring to a slow boil over medium heat.
Make a slurry with 2 Tablespoons of cornstarch and 2 Tablespoons of water. Mix well and pour into skillet. Stir over medium heat until gravy thickens.
Reduce heat to low and add salisbury steaks back into skillet, spooning mushroom gravy over the top of steaks. Let patties stay in the gravy for a few minutes to absorb the flavors.
Serve hot over mashed potatoes.
Notes
Storage and Freezing
Store leftovers in an airtight container in the refrigerator for up to 3 days.
Freeze leftovers for up to 3 months in an airtight container or freezer bag. To thaw, do so in the refrigerator overnight.
Reheat leftovers in the oven or microwave until the internal temperature reaches 160 degrees F.