I'm a big fan of the pescado (that's fish) sandwich. Make sure to drench it liberally with whichever salsa you prefer from the salsa bar, and you won't be disappointed. Note that it can get pretty busy here around lunchtime (especially on nice summer days), so consider coming on the early side if you don't want to wait in line forever.
I only have one minor complaint with the establishment -- parts of the bread sometimes come out pretty burnt (and burnt food is a suspected carcinogen). But, you have to balance that with the deliciousness, so I figure it's worth it once in a while!