...Oh, and always wrap a hero in plastic and allow to come to room temperature for an hour or so for the best flavor. The irony of cold cuts is that they are not meant to be eaten cold.
I had no idea.
It's the fat, it needs to come to room temperature for best flavor. Or you could give it a quick turn in a low temperature skillet. I worked at an independent Virginia Beach sub/pizza shop as a kid. We made premeasured, prewrapped sandwich selections, and once we got an order, we unwrapped it and threw it on the grill for about 5-10 seconds, then slapped it into the hero with all the rest of the fixings. For some reason, the owner called it 'Philly style'; I have no idea why, but maybe it had to do with the way they make cheesesteaks there, I just don't know. But I do know that rather than messing up a skillet, I make the sandwich and wrap it up and let it sit on the counter to warm. That's why Italian hero sandwiches made ahead of time for a picnic always taste better than ones made and eaten immediately. By using oil and balsamic, you don't have the mayo issue to worry about, either. Also, I'd use sun dried, not fresh tomatoes as they are too wet, and can make the sandwich soggy; you can always make a sun dried tomato/black olive/roasted garlic paste, which would be fine. Roasted peppers can be moist, too, but they have less water. And never use fresh mozzarella, much too wet. Tastes good, but be prepared for a drippy mess. That's why I use the hard imported provolone and slice it myself; the slicing provolone is too waxy and has little flavor.
Heating a sub is why Quizno's is so popular. In college, the local sub shop/bar threw the sandwich in a toaster oven for a minute or so, again to warm the meat up and slightly melt the cheese. But I'm beyond that now. LOL! Having it at room temperature is plenty good for me. Plus, it's less work and cleanup -- including clothes as no runny fat is dripping all over the place.