Opening a restaurant tests the resilience of the most optimistic entrepreneurs. Alvaro and Andres Sandoval, brothers and co-owners of Tenoch Mexican, a popular Medford eatery, found this out when they proposed a second location in the North End. When one of the neighborhood councils, serving in an advisory capacity to the city zoning board, voted against the brothers’ plan to move into a tiny space on Lewis Street and offer take-out, it was a low moment. “They thought we were fast food, and that was disappointing,” says Alvaro Sandoval. But the brothers, who come from Veracruz, Mexico, and cook their family recipes, were determined to win over the naysayers. It’s not surprising that the second location is as popular as the first. The proof is on the plate.