Definition of "Sushi"

Then there are the "Sushi" neighborhoods and towns - a mixture of some Sunni, some Shia, hence Sushi

2007, Francis X. Callahan, Does W Stand for Worst?: The Record of G.W. Bush - Page 160

... particularly from the Sunnis you talked to, and the Shias were always angry. (Ali calls himself Sushi so it's kind of a mixture.)

2007, John Palattella, Reporting Iraq - Page 173

Reality proved quite different. Ahmed is half Sunni, half Shia—a “Sushi,” in his own words

2010, Paul Wilson, Erasing Iraq: the human costs of carnage - Page 34