For the pork:

Cut the pork into 2 inch thick slices.

In a bowl combine the achiote paste, bitter orange juice, oregano, cumin, garlic, salt and pepper.

Whisk until the achiote paste is fully dissolved.

Place the pork into a large ziploc bag and pour the marinade over.

Refrigerate for a minimum of 4 hours or overnight.

Put the pork and marinade in a slow cooker.

Cook on high for 4 ½ - 5 hours or until the pork is fork tender.

Remove the pork from the slow cooker and let cool for 15 minutes.

Using two forks, shred the pork.

Place in a serving bowl.

Pour the remaining marinade from the slow cooker over the pork and stir to combine. If not using immediately, cover and either refrigerate or freeze.

For the onions:

While the pork is cooking, combine the onions with the Naranja Agria and salt in a small bowl. Cover and store in the refrigerator for up to 4 days.

To assemble the tacos:

You can use the tortillas as they are, or you can char them over a gas cooktop or on the grill.

Fill with ¼ cup of the pulled pork, top with some of the marinated red onions,cotija cheese and cilantro.

Serve!