I had never even heard of a "torta"... essentially a Mexican sandwich... before a year or two ago: it's more street food that anything else, so you're unlikely to see it in a sit-down Mexican restaurant and our Mexican fast food up here in New England is totally burrito dominated. In fact, I suspect if I put a hallowed out roll filled with carne asada and guacamole in front of some people they'd assume I was "Americanizing" traditional Mexican cuisine.... as if they don't have bread in Mexico. Not everything "authentic" has to be wrapped in a tortilla guys.
Regardless of any tiresome authenticity debates... tortas are awesome. This particular vegetarian recipe is from Rick Bayless, and was featured on Serious Eats a week or so ago... which is where you can find the recipe itself. The highlight of the dish for me was definitely the mushrooms... the technique of roasting them with citrus being something I'd like to experiment with separately: they were absolutely fantastic. On the slight negative side, I thought our goat cheese was a little strong and overpowered some of the other flavors with a full ounce (Anna did not agree with this). As in all things, just use your judgement.
We didn't get nice bread here, settling for simple supermarket whole wheat hoagie rolls... and they worked fine... however, you might be better off with bread with a harder crust. It will hold up better during the scooping out of the bread guts phase.
One highlight of the methodology is that it works just as well with cold ingredients pulled from the fridge as it does if you are doing it all in one go to get food on the table ASAP.... so leftovers are great. Since you heat up the bottom half of the torta with the the mushrooms and refried beans for five minutes in the oven (plus another 2 minutes with the top, goat cheese, arugula, and salsa) the sandwich is delightfully toasty and warm regardless.