I'd never heard of the the Ontra Cafeteria, and it's not like there was only one. There were five in L.A./Hollywood/Beverly Hills (plus one in Chicago). Here's what is apparently Stephen Sondheim's memory of the Beverly Hills Ontra: "My mother and I would argue endlessly about the pronunciation of said Ontra Cafeteria. She thought it should be pronounced On-truh and I was convinced it was On-tray, a logical assumption since the food was served on a tray. We never came to a meeting of the minds, but we did love our meals there. There was something exotically wonderful about eating in a cafeteria."
While there is some discrepancy as to the labeling of the interior shots below, it seems that, clockwise below, are the Wilshire, Crenshaw, Vine and Vermont locations.
265 N. Beverly Drive
A later interior remodeling of the Vermont location
More info:
Los Angeles Times
Pics: Top,
Zilf; 265 N. Beverly:
O.C. Tax Atty; all others:
Ebay