CHELMSFORD — Gene Wu didn’t plan on a noodle-pulling career. The effusive proprietor of Gene’s Chinese Flatbread Cafe came here 15 years ago from Xi’an, the capital of northwest China’s Shaanxi province, to study chemistry and find steady work. Now Wu toils happily at a small storefront, stretching noodles behind a counter. Hand-stretching noodles is an arduous process that rewards only those who appreciate sunrises. Still, Wu saw an opportunity: While Western Chinese restaurants like Xi’an Famous Foods are making waves in New York, Massachusetts lacks authentic Xi’an cuisine, hallmarked by noodle soups and flatbread. “In northwest China, we didn’t have much rice,” he explains.