Thanks to Kirkk, I found out about Torta Factory on El Cajon Blvd and experienced cemita bliss today for lunch - quite on the level of Cafe Dore/ Paris Bakery Banh Mi.
I had the cemita de pata - fresh toasty nutty sesame roll, wonderfully pungent papalo herb, rich panela cheese, bright jalapeno/onion escabeche, avocado smear and homemade oregano flavored pata.
I love this sandwich!
There is a bakery on 30th and Imperial that makes them but the time i tried it was just 'meh' and they lack the essential papalo.
In Tijuana I know a place that just makes about 20 varieties of cemitas but I dont know if you are afraid to or willing to cross the border.
Probably 99.9 percent of the people reading your post have no idea what you are talking about (including me).
I found this in wiki:
"A cemita, also known as a cemita poblana, is a Mexican sandwich and street food that originated in the city of Puebla.
It is distinguished from a torta by the fluffy sesame-seeded egg roll that it is served on. Additionally, the ingredients usually are restricted to sliced avocado, meat, white cheese, onions and red sauce (salsa roja). Recently it has appeared on the streets of New York, Los Angeles, and other cities with Mexican food vendors.
The most popular meat in a cemita is beef milanesa, a thinly pounded and deep-fried piece of beef. Cueritos (pickled pig skin), queso de puerco (pork head cheese), and carnitas (stewed pork) are also popular. The cheese is often panela, a bland white cheese with the consistency of fresh mozzarella. Quesillo, a Mexican string cheese, is also used."
Mexican sandwiches (i.e., tortas) are not big in San Diego. However, there is La Torta chain (http://www.latortamexicandeli.com/) with three establishments in San Diego. ( Cemitas are not listed on the menu)
Perhaps if you become friendly with someone at one of the establishments, they might be willing to create a makeshift equivalent of the sandwich you so seek.