It’s the lunch rush on a busy Wednesday at Dengeos in suburban Skokie. The restaurant’s menu reads like the guest list for a party dedicated to fans of Chicago greasy spoons — mustardy hot dogs, Italian beefs, Polish sausages and mostaccioli abound. And, of course, gyros. Dengeos is a Greek restaurant first and foremost, and it’s been serving up the yogurty, salty pita pockets since 1972. Behind the counter, between the shuffle of cooks and kitchen staff, Dengeos owner Nick Theodosis shows off the key to the joint’s long-running success: three large machines, each with its own cone of rotating,...