My local favorite is still Javier's--I like the Crsytal Cove location better, but the food is just as good at the Irvine Spectrum. The only downside is that they are always busy.
their saltenas are goooooooood (http://rollies.weebly.com/bolivian-menu.html picture here)
I love their tacos too (they have got EXCELLENT asada, really flavorfula nd well seasoned) although i'm not sure if they cater them.
Stop by there and order a saltena and a taco and whatever else you want to try.