Here are two good informal spots in Costa Mesa and Newport Beach which should please chowhounds:
El Chinaco. Great pupusas. Very tasty curtido (the cole slaw you put on top of the pupusa). On Harbor Blvd. about two blocks north of 19th street. On the west side of Harbor, next to the car wash.
Las Carnitas. On Newport Blvd. just as you come onto the Balboa peninsula, on the right side, just afer Lido, across from Bank of America & Starbucks. This place really makes a great plate of Cal-Mex food. And cheap too.