Los Nopalitos (República de Uruguay 219, tel. 504/221-0684, noon–11 p.m. Tues.–Sat., 10 a.m.–5 p.m. Sun.), on a side street not far from the U.S. Embassy, is hands-down the most authentic Mexican restaurant in town. Three-course lunch specials plus beverage are available Monday–Friday for US$10, but the best time to visit is for a weekend lunch, when Mexican specialties such as cochinito pibil (Yucatan-style pork) or barbacoa de borrego (lamb barbecue) are prepared.
For inexpensive Mexican breakfasts, tortas, tacos, burritas, tostadas, and garnachas (US$2–4), try Tortas Locas, on the peatonal, or Turimex, a block east of the parque on Avenida Colón (the latter also offers licuados).
Los Cebollines near Mall Multiplaza is a pricier Guatemala-based chain in an atmosphere like a Mexican-style Tony Roma’s (which happens to be next door), but the food is actually good and the margaritas are great.