I picked up a veal and eggplant parmigiana sandwich the other day and I was impressed. $8 gets you a huge sandwich that's guaranteed to satiate even the largest of appetites.
I went during off-peak hours, so the line wasn't too bad. There was a line of approximately 10 people an hour earlier. Even with the line, service is pretty quick and efficient. Friendly? Maybe not so much.
I believe Uno Mustachio excels in its breading and deep frying. Both the veal and eggplant are thinly sliced and breaded. They maintain excellent crunch without being too greasy.
Like others have mentioned, I'd opt-in for the hot peppers. They really add a much appreciated heat element to the sandwich. The peppers also add some moisture to the sandwich. A common minor complaint is that the sandwich is a bit on dry side. Asking for peppers or extra sauce helps.
Overall, a very good parmigiana sandwich. I don't think it gets much better. I still give the nod to California Sandwiches, since I enjoy their red sauce and freshness. Sometimes I feel the sandwiches at Uno Mustachio end up sitting under the heat lamp and lose some flavor as a result. Try to get a fresh one.