So the other day I was complaining to one of my students (who's from LA) about how challenging it is to find decent Mexican food in Taipei. She turned around and told me that I should try El Sabroso (address: 107, Section 3, Tingzhou Road; telephone 02-2368-9599; closest MRT access is Taipower Building Station via Exit 1; it's also an easy walk from Gongguan Station and the night market zone).
Here's what I found: a hole-in-the-wall shop, with five counter seats and a friendly vibe. An amiable Mexican man named Oscar prepares the food; a friendly bilingual (and perhaps multilingual) woman handles the orders. Highlights so far include substantial burritos (the one I had tonight with asada totally rocked--be sure to ask for the salsa to be put inside); impressive quesadillas, packaged in a smart looking box; delicious orchada served with the sets (NT$210 for a burrito and drink or a quesadilla and drink; NT$185-195 for just a burrito or a quesadilla). I've been told their taco Tuesdays are a hit--though I've not yet tried them. Same with the nachos, which some regulars are evidently fond of too.
With fresh and tasty food prepared and served with warmth, this place is an fantastic addition to the Gongguan neighborhood. Closed on Sundays; open other days until 7:00pm (if you will arrive late, you can apparently call in advance to place your order).