In a small bowl combine the salt, herbs and spices for the meat.
Slice the meat thinly against the grain and then pound with a meat mallet to less than 1/4-inch thick.
In a flat-bottomed container, arrange one layer of slices, sprinkle with vinegar or lemon juice and then liberally with the seasoning mixture. Repeat in layers.
Cover and refrigerate for at least one hour and preferably overnight.
Dry fry the meat (without any oil) in a non-stick frying pan until browned and slightly crisp or broil on the grill.
Brush the pita bread with olive oil and fry in a dry frying pan or grill for a few minutes until warmed and softened, not crisp.
In the center of each pita spread 1 heaping tablespoon of tzatziki, add 2-3 slices of tomato, sliced onion to taste and the gyro meat.
Twist the gyro sandwich in butcher's paper, parchment paper, or wax paper and serve.