Yesterday I chanced upon a truck at Santa Monica and Bundy (NE corner) serving "cemitas poblanas autentica". It is run by one Pedro Martinez and while I can't vouch for his fastball the sandwich estilo Puebla was excellent.
I ordered the milanesa - an expansive flattened steak breaded and fried, the breaded foodstuff in a sandwich is amusingly self-referential - which as per the hand lettered sign also contained:
papalo - Mexican coriander
aguacate - tons of sloppy, ripe ripe avocado
chipotle - vinegared whole chillies, pitched somewhere between Cholula and Isaan/incapacitating on the hotness scale.
cebollas - raw onions
quesillo - piles of stringy white cheese. See Harold McGee's excellent "On Food and Cooking" for a scanning electron micrograph of this stuff.
The roll was high-domed, round, sesame-seeded and crunchy as it should be and the gestalt a delicious meal well worth the $5 (at the high end for truck fare).
Also tried the atole which was just OK, I prefer mais to arroz con leche even though it did contain whole cinnamon sticks.
I'll be coming back to this truck which according to signage should be there from 6pm to 1am. There are tacos/burritos/other cemitas/tlayudas to try. Perhaps this is another case where pretty good Mexican fare can be found west of La Cienega if one wanders aimlessly enough.
Low End Theory