"Cinco de Mayo is a regional holiday in Mexico, and commemorates the Mexican army's unlikely defeat of French forces at the Battle of Puebla on May 5, 1862. While Cinco de Mayo has limited significance nationwide in Mexico, the date is observed in the U.S. as a celebration of Mexican heritage and pride." (Ref. Wikipedia).
The RED (not ED) ONION Mexican Restaurant is a peninsula tradition, and has been in business since 1963 at the same location on Silver Spur Road. Originally opened by the restaurater Bart Earle and his wife, Joanne, it was purchased by Bart's son, Jeff in 1995. In the '60s, it hosted daily fashion shows, and mariachi bands that played until 2 AM. My in-laws always enjoyed dining there and many who grew up in the South Bay remember eating there as children.
(The info & the 70's photo are from Rolling Hills Estates: 50 Years of Country Living With Style.)