You don't have to or need to cook pastrami before eating it.
The pastrami is already cooked because the pastrami you buy in stores goes through a smoking process that smokes the pastrami and cooks it while it smokes it.
So you can eat the pastrami cold or heat it up.
It doesn't take long to prepare the pastrami because it doesn't require much time to heat it up.
There's no need to cook it like you would other meat because the pastrami is fully cooked and ready to eat.
You just need to heat the pastrami up before you eat it or serve it if you want too.
The pastrami does not require being heated up first but the pastrami in my opinion is more enjoyable after being heated up.
But you can use cold pastrami to make sandwiches or just eat the pastrami cold if you prefer it.