I was standing on the sidewalk waiting my turn at Tacos La Guera , a street vending stand that sets up each evening between a Whole Foods parking lot and the four lane cacophony that is Lincoln Boulevard. “How many tacos?” a young man named Rafael asked me, pressing a 12-inch chef’s knife against a massive cone of al pastor pork crowned with a pineapple. I passed on the pork and asked for a quesadilla, which means another cook tossed shreds of white cheese directly on a sizzling flat top where it instantly melted, topped it with a flour tortilla,...