Toast the cumin and coriander seeds in a small skillet over medium heat, swirling the pan, until slightly darkened, about 2 minutes. Transfer to a large bowl. Add the vinegar, olive oil, garlic, red pepper flakes, cinnamon stick, brown sugar, chile powder and tomatoes; whisk to combine. Put the lamb in a large nonreactive container and add the marinade; cover and refrigerate overnight or up to 48 hours.
Preheat the oven to 350 degrees F. Remove the lamb from the marinade and pat dry; reserve the marinade. Season the lamb with salt and pepper. Heat the canola oil in a large Dutch oven over medium-high heat. Working in batches, add the lamb and cook until browned, 3 to 4 minutes per side. Add the reserved marinade, the beer and jalapeno and bring to a simmer. Cover, transfer to the oven and braise until very tender, about 2 hours. Remove from the oven and let cool slightly. Skim off any excess fat. Remove the lamb and pull the meat off the bone, discarding the bones and fat. Strain the liquid into a smaller pot and keep warm. Shred the meat with your fingers and transfer to a bowl. Pour the warmed braising liquid over the meat and toss to coat. Divide among corn tortillas and top with cilantro. Photograph by Charles Masters
Recipe courtesy Michael Symon for Food Network Magazine