Javier Diaz de Leon, consul general of Mexico in Atlanta, introduces chefs from Merida at Atlanta's No Mas Cantina. In 2010, traditional Mexican cuisine received UNESCO World Heritage designation as a cultural treasure, but the joints that serve most Americans must not have gotten the memo.Many serve a half-baked version featuring beef and chicken as the main proteins, accompanied by cheese, tortillas, rice and beans in a dizzying array of combinations labeled numerically to make ordering simpler. Burrito chains bring another uniquely American dimension, and while they may be wildly successful from a commercial . . .