I just grilled up a steak marinated in vinegar, rosemary, and olive oil. Problem is I made too much. What's the proper way to freeze, store, and subsequently reheat this steak to get it as close to as delicious and tender as it now?
I'd recommend letting it cool to near room-temperature, then place it in an airtight sealed plastic freezer bag before it dries out too much. You can spoon some of the juices from cooking into the bag with the steak so that when it defrosts again the juices will be in there working to keep it moist.
When you defrost it, do so in your fridge leaving it overnight so that it defrosts gradually, keeping it in the freezer bag so it doesn't lose any more moisture. It should then be good to reheat, probably best in a shallow pan rather than a microwave to retain moisture.
My favorite way to handle this situation is to allow the steak to defrost in the refrigerator and then slice it thinly for a steak sandwich with provolone cheese.
Generally speaking, you don't.
If you really must freeze steak, freeze it before cooking and slowly defrost it in a collander overnight.
Re: your current problem - I would wrap in tinfoil and heat in the oven. A pan may overcook it.
In general, you can't (just to back up the other answers). But you can do other things with the steak!
Update: My wife says that while it's not ideal to freeze it after cooking, you can use a vacuum sealer (if you have one) to help reduce the chance of frosting, and keep the moisture in as it thaws. Zip-Loc is also selling a bag that's supposed to do much of the same, but we haven't tried it. But getting as much air out as possible is the key.
First wrap in foil. You don't want plastic anywhere near your steak if you can help it to avoid that plastic frozen dinner taste. Then wrap airtight in plasric wrap - not plastic bag.