Funny, we stumbled upon the same place today!
We had just dropped the car of with the mechanic for a maintenance session and were on our way to the MRT for our first visit to Macho Nachos when two doors next to the garage we saw this new place:
facebook.com/pages/Cactus-M … 5807351411
400 Sec. 3 Heping E. Rd. Da’an Dist., Taipei,
Phone: 223773525

Cactus is new, it only opened in January, the cook/owner is Mexican, and we really enjoyed our meal.
I had the Nachos and Beef Enchilada, and hubby had the Taco.
Nachos were strange, instead of melting cheese on top they use a cheese/milk sauce. It did not do it for me, and I mentioned this to the English speaking waitress/owner (who might have heard this before as she immediately asked if it made the Nachos too wet).
However, the good thing was that there was plenty of cheese sauce and toppings!
That was my only grumble about the food!
The rest of the food was Mexican (not tex-mex), so cheese was not an issue.
The Enchiladas were beautiful, the beef was cooked perfectly and NOT dry, and covered with an interesting red chilli sauce (not spicy, slightly sour).
Hubby was happy with his traditional tacos, and both meals came with rice, re-fried beans and extra tortillas.
Service was friendly and even though we were the only ones when arrived, it soon filled up!
We will be back (next time we need to get work done on the car)