When Washingtonian named the three guys behind Cava its Restaurateurs of the Year back in 2010, there were only two outposts of the Greek spot-Rockville and Barracks Row-and it was a sit-down eatery, not a fast-casual chain. The vibe and cuisine were worth seeking out, the magazine wrote, but “whether there will be a third Cava . . . the owners aren’t saying.”