In a large bowl, combine ground beef, egg, minced garlic, panko breadcrumbs, oregano, soy sauce, Worcestershire sauce, ketchup, Dijon mustard, salt, pepper, and the prepared onions. Mix well and set aside.

Divide the mixture into 4 oz portions. Shape each portion into a steak-like patty.

Heat oil in a frying pan over medium heat. Cook the Salisbury steaks in batches, for about 2-3 minutes on each side, or until cooked through. Remove and set aside.

In the same pan, melt 1 tbsp of butter. Add the chopped onions and mushrooms, sautéing until the mushrooms begin to soften.

Add another tbsp of butter along with the minced garlic. Sauté for 30 seconds, then sprinkle in the flour and black pepper. Cook for 1-2 minutes, stirring constantly.

Stir in the beef stock, ketchup, Dijon mustard, and Worcestershire sauce.

Return the Salisbury steaks to the pan, along with any resting juices. Simmer until the gravy reaches your desired thickness.

Stir in fresh parsley and adjust the seasoning with salt and pepper.

Serve the Salisbury steaks smothered in mushroom gravy, garnished with more parsley. This dish pairs wonderfully with mashed potatoes or steamed vegetables.