Season the meat evenly on both sides with salt and pepper. In a braising pan with high sides, heat the oil over high heat. Add the ribs to the pan and sear on all sides until browned, about 1 minute per side. Pour in the beer and add the tomatoes to deglaze the pan. Cook, stirring, for 2 minutes. Add the tomato paste, chiles, tamarind paste or Worcestershire sauce, garlic, orange zest, brown sugar, canela or cinnamon, bay leaf, allspice, thyme, and beef stock. Decrease the hear to low, cover the pan, and simmer until the meat can easily be pulled from the bone with your fingers, about 4½ hours. Don't overcook the ribs, or the meat will be mushy. Shred the meat and serve immediately or keep warm in the pan until ready to serve. 

To serve, lay the tortillas side by side, open face and overlapping on a platter. Divide the filling equally between the tortillas and top with onions and salsa. Grab, fold, and eat right away. Or build your own taco: lay a tortilla, open face, in one hand. Spoon on some filling, top with onions and salsa, fold, and eat right away.