Tacos al Carbon is a good dish by which to judge the authentic Mexican food at a restaurant. Prepared with different spices than fajita meat (but usually with the same cuts), I usually look to see how close a restaurant comes to some of the taquerías in El Paso and southern New Mexico. I recognize that there are regional differences, but Diego's is one of the few places I have found in Oklahoma that comes close to the authentic Mexican version. By "authentic," I mostly mean flavorful meat with good spices and side dishes. Diego's serves the tacos on flour tortillas, while I think most authentic versions would have corn. This can be easily fixed, though, by ordering corn tortillas that come at no extra cost. Everything else I found to be quite good, with the guacamole and pico de gallo being especially good. I do not put sour cream on my tacos (I think this is a Tex-Mex adaptations), but customers are free to use it or skip it. I think I am pretty safe in saying these are some of the best tacos in Oklahoma City, or at least north OKC. If I find ones that are better, Diego's will be my first point of comparison.

Chile relleno plate

The Chile Relleno was kind of a gloppy mess with melted yellow cheese on top, and I find it hard to find ones I really like compared to the ones that come from the Rio Grande Valley. The one at Diego's was no exception, although it was better than many served in Oklahoma. Since rellenos are commonly served in Tex-Mex restaurants, I think this is one case where the restaurant made the food Tex-Mex style.

Diego's serves fresh Mexican drinks such as horchata, but was out when I went (on a busy weekend evening, when I would think they would have enough customers ordering it to make another batch). I did get the sense that the "real" Mexican food was available but limited in what could be ordered (if someone wanted beer instead of horchata they would have been fine). At least Diego's authentic menu is less limited than most restaurants in north OKC.

The main drawback to Diego's seemed to be that it was such a dive it made the experience less comfortable than it might otherwise be. Located in a former fast food restaurant, the tables and chairs looked as if they had had quite a bit of use. The bathroom had a plumbing leak, and I would describe the whole place as pushing the limit of being in disrepair (although it did not seem to be dirty). I thought the food was good, and they obviously have a good kitchen. The fact that they ran out of drinks and the bathrooms were not repaired, though, showed that they might have some customer service issues.