I just happened upon this site. I too use to live in EL Centro from '59 until the early 70's. I have so missed "special" quesadillas and have searched off and on over the years for a recipe. I miss La Hacienda down to the cheese that was used on their tacos. I don't know what kind it was, but no taco since has tasted right without it.
There use to be a place near IVC called something like Tiki Hut, that had some of the best food ever.
I would adore finding some of these recipes.