Scoop the onions into a glass bowl. Pour enough boiling water to cover the onions, wait one minute, and then pour the onions into a strainer. Return the drained onions to the bowl, add the lime and orange juice, and stir in the salt. Cover and set aside until serving time.

The onions will last for a week or more in the refrigerator.

Place the onions and garlic in an even layer in a slow cooker and pour in the chicken broth.

Combine the sugar, chili powder, salt, cumin, and cinnamon in a small bowl. Pat the pork dry with paper towels.

Rub the yellow mustard and spice mixture all over the pork and place the meat on top of the onions and garlic. Cover and cook until the pork is fork tender, about 6 to 8 hours on medium-high.

Turn off the slow cooker and transfer the pork to a cutting board.

Set a fine-mesh strainer over a medium heatproof bowl. Pour the onion mixture from the slow cooker through the strainer and return the solids to the slow cooker. Set the strained liquid aside.

Remove and discard the bones. Using 2 forks, shred the meat into bite-sized pieces, discarding any large pieces of fat. Return the shredded meat to the slow cooker, add the barbecue sauce and mix to combine.

Taste and season with salt if needed.

Place pulled pork on bottom halves of ciabatta rolls. Top the pork with pickled red onions. Cover with the top halves of the rolls and serve.