The Zephyr Theatre!
I was in there exactly once, in the late 1970s, to see a friend perform in a play called BAGEL INCIDENT by Samuel Gerstein, about which I remember exactly nothing. At the time, my friend worked in one of my regular Beverly Hills lunch haunts, Bon Appetit on Beverly Drive. I hadn't remembered the horseshoe seating, but the one picture on their website brings it back well enough. Miraculously, the program survives. It contains ads for Fellini's, which I'm not sure I was ever in, and Posh Bagel and Bagel Nosh (do you detect a pattern here?).