I'm not one for throwing out self-made recipes, but here's a pretty good way to have a hot pastrami sandwich.
First, chop up some onions and saute them in olive oil and butter. If you've got enough time, you could caramelize them, but it's enough to just brown them and soften them up. Meanwhile, simmer the pastrami slices in a cup of beef broth. Once the onions are done, throw half your pastrami slices in the pan, then add a couple of slices of cheese (I used muenster this weekend, but use whatever you like), and then top it with the rest of the pastrami. Cook it for about a minute, and then flip it over. Cook until the cheese is melted. Put that bad boy on some bread, top with the onions, and enjoy the deliciousness.
If you're curious, this sandwich could be anywhere between 400-600 calories depending on how much of each ingredient you use - mine tipped closer the 600 mark.