Re heat the birria according to package instructions. Remove the beef with a slotted spoon and reserve the juices from the meat
Dunk the corn tortillas in the meat juice and coat both sides evenly
In a skillet over medium heat, add the tortilla and add 2 spoonfuls of cheese and 2 spoonfuls of meat to one side.
Fold the tortilla in half and cook for about 2 minutes until the cheese starts melting.
Flip the taco and cook on the other side for another minute or two. Serve tacos with chopped onion and cilantro on top and a side of the meat juices for dipping