We walked to El Parnaso for a late lunch after touring El Morro. There was limited outdoor seating, but we didn't want to sit inside, so we waited for a table to become available. The GF menu options were limited. My husband and son loved their meals, but I thought mine was only ok (mine was GF). Prices seemed a little high for what we had, but I didn't get sick. :-)
Great/inexpensive little place for Mexican food! They have corn tortillas, but you have to ask for them.
After touring the fort in San Juan, my husband and I were walking back to the hotel down Del Cristo road. We decide to stop for a drink and ended up at "El Parnasos Mexican Restaurant Bar" (which had outdoor seating). After sitting there for a bit I started talking with the waiter. We ended up ordering nachos. Everything on the nachos was gluten free. I was a little scared to try them. But was assured they were ok. I ate them and the nachos were good. I can not tell you about the rest of the menu. But if you just want a snack or something to hold you over till the next meal, try the nachos. They were very good. The drinks were very good too.