Those with high cholesterol beware of the Torta. It takes no prisoners...
It's good to be back in the land of good Mexican food. Napa Valley is over 65% Hispanic and there are great local markets, such as La Luna and Azteca Market, that don't mess around. Both usually have lines around the block during lunch so go during off hours. La Luna is a store I have been going to since I was a kid. I used to ride with my friend from her nearby vineyard (now a HWY 29 hot spot by the name of Peju Province) on their 3-wheeler to grab lunch and go to their nearby stable and ride horses in the afternoon. They sell everything from hot peppers to wedding dresses. It's a town gem.
Regardless of my history with tasty Mexican cuisine, it's hard to go a long day of hard work in the Valley without filling up on a torta. Now, these are no joke. Beginners should split one. They don't mess around and Mexican food is never good left over. You MUST eat on-site. Take-out is for rookies and drunks.
If you cannot find this sandwich locally at a Mexican or Cuban joint than try to make it at home after a day of some hard labor or if you are just in the mood. Tortas are a pretty generic term so basically all you you need is to pick a protein (beef, pork, shrimp, fish...) and choose from refried beans, scrambled eggs, milanesa, chipotle, avocado, sour cream, lettuce, jalapeño, tomato, and cheese. The bread is key so expect a nice soft white roll with a house sauce (red or green). Also, if I were you, I'd add spice wherever possible.
Enjoy your next (or first) Mexican sandwich.