Weekends, this metal-clad taco wagon near busy St. Elizabeth Church in Fruitvale offers barbacoa, lamb cooked so long the meat falls away into savory, tender strands. You can have it heaped in tacos, order the thinned-out cooking juices as consome (with chickpeas, sprinkled with chopped cilantro and raw onion) but we love it best in a Guadalajara-style torta ahogada, or wet sandwich. Get it spicy (picosa), and what emerges from the wagon’s order window is a lamb-filled roll bathed in chile-spiked meat juices. You sit in one of Pipirin’s plastic patio chairs under the backyard pavilion tent, your mouth burning, in a race to finish before the soaked bread turns soft as custard — this is a torta as much about the experience of eating it as it is about the sandwich itself. Don’t forget to wash the lamb juices off at Pipirin’s makeshift hand-washing station, a water jug with spigot, wedged in the taco wagon’s hitch.