Ed Fernandez in Nestor serves the best single thing you can eat in this county, and it is birria — the meat, a bowl of broth beside it, and a room full of people who all made it there before the 2pm close.
Nothing else here looks anything like that, which is the honest state of eating in San Diego. Twelve orders that between them take in the border, the Pacific, a Filipino steam table in National City, a Hawaiian counter in Ocean Beach, a butcher in Cardiff, and a pie shop an hour inland. Several of them get eaten standing up in a parking lot. Two of them — carne asada fries and the California burrito — were invented in this county rather than imported and improved.
The dessert is a drive. Julian is a whole Saturday rather than a stop, and that turns out to be the correct amount of effort for the pie.
Do not try to run all twelve in a day. Fries go soft, sushi rice goes cold, aguachile stops being cold at all. Pick two that are near each other and give them the afternoon.
For more depth inside one category, use the guides to San Diego tacos, burritos, fish tacos, and sushi, or the wider best restaurants in San Diego. Pair the National City stops with the National City neighborhood guide, or build an Ocean Beach afternoon around the Ocean Beach guide.