Forget La Verdad. Forget Anna’s. Forget that tiny café whosit in Eastie that the Chowhound faithful have anointed the Mexican-food messiah. The city’s burrito comes from a no-frills storefront in Downtown Crossing that specializes in quick lunches for slumming-it bankers. It’s the handful of non-gringo grub (ignore the turkey wraps) that sets this dive apart, led by the al pastor burrito, a masterpiece encased in a well-griddled flour tortilla. Unlike its lesser competitors, Burritos Express understands that rice, beans, cheese, and guacamole are supporting players that should never upstage the star: fiery, chili-marinated, deeply charred chunks of pork.