If yours isn't coming out so tender (assuming you're not trying to cook up the old rooster), most tough chicken problems are from inattention to temperature, overcooking. There are two issues. One is making the piece of chick equally thick throughout. Chicken goes from just right to real wrong in a very short time. You're aiming at 160F throughout, but if it's thick in one part and thin in another, you can't get one part right without getting the other underdone or overdone. You get it evenly thick by pounding it, which also somewhat tenderizes. But the main thing is to make it evenly thick.
Then, of course, you have to hit the 160F pretty close, without going over and overcooking it and making it tough. That's the so-called safe temperature for chicken. So you need an accurate meat thermometer. Remove the chicken when it hits 160F internally. Don't just turn the fire off or remove the pan from the stove.
I don't know how that restaurant operates, but a lot of restaurant cooking is done sous vide, low temperature, in vacuum sealed bags, in a water bath. In sous vide, the reality that tenderness and doneness are entirely different things comes home. You can take a meat, say chicken, to 160F in a sous vide water bath, and it will be done and will never get hotter and so will never get overdone. (You can really see this with beef, where beef in a 125F bath will be medium rare and stay medium rare, even if left in for hours.)
Tenderness is a matter of cooking time. (Unless the meat is already tender, like filet.) You can make a tough cut tender and still rare by loooong cooking at low temperature. Slow cookers work that way, except that the temperature is so high that all the meat comes out well done. The point is that a restaurant can prep chicken cuts in a sous vide bath well ahead of time. They won't have to pound, either, because the bath will be 160F, and that's as hot as the meat can get. If they want a piece, they fetch it out and use it or put grill marks on it. They just can't leave it in there as long a they do some beef, because it will start to fall apart. But it's very efficient, and it kind of explains some of why you can get a steak so quickly in some places.
Just a note. Brining, marinating, etc. do not tenderize. Marinades penetrate only a tiny fraction of an inch. Brining uses salt to move water around, and moist is not the same a tender. It's just that people who bother to brine are also generally more careful cooks and done overcook.
All that said, some of the restaurants you named are said to do their cooking from frozen boil-in-bags of precooked food, and they are all in the class of place I would suspect of doing so. This is not sous vide. It's boil-in-bag like you buy in the store. Check Yelp and try a real Italian restaurant near you. Why pay even cut-rate restaurant prices for frozen entrees? The chains simply cannot afford real cooking by real chefs. The Tuscany chef training is an advertising myth. Note that the brand new Italian Garden parent company CEO commented that he knew changes were in order when he learned they didn't salt the water for cooking pasta. He may have misunderstood. They don't need to salt the water if the pasta is precooked in a bag.