Prepare the Salisbury steaks by mixing together the beef, egg, tomato paste, mustard, Worcestershire sauce, garlic powder, bread crumbs, salt as desired, and pepper.
Divide the mixture into 4 equal parts, shape into patties.
Heat a splash of olive oil in a large non stick pan, add the patties and cook for 4 to 5 minutes each side until well browned. Remove from the pan and set them aside.
In a small sauce pan, prepare the gravy packets per the package instructions.
Using the pan you cooked the patties in, add the onion, mushrooms, and thyme. Saute until the onion is translucent and soft, and the mushroom well wilted and starting to brown. Reduce heat to a low simmer and pour in the gravy from the sauce pan and stir in the soy sauce.
Add the patties to the gravy, cover and cook for 10 minutes.
Turn the patties over, cover and cook for another 5 minutes or so, until cooked through.
Season the gravy to taste with salt and pepper as desired, serve with mashed potatoes or egg noodles.