Season pork with salt and pepper; set aside.

Heat oil in a large pot over high heat.

Add pork in batches so as not to crowd the pot and cook, stirring occasionally, until browned on all sides, about 2 minutes per side.

Using a slotted spoon, transfer pork to a large plate as done.

Discard all but 1 tablespoon fat from pot.

Reduce heat to medium low and add white onions.

Cook, stirring occasionally, until starting to brown, about 4 minutes.

Add garlic and bay leaves and continue stirring until fragrant, about 2 minutes.

Return pork to pot and add orange juice, lime juice and 1/4 cup of the vinegar.

Bring to a simmer and season with salt and pepper.

Cover, reduce heat to low, and cook for about 1 hour, stirring occasionally, until pork is very tender and can be easily pulled into shreds.

Meanwhile, separate red onion slices into rings in a large bowl and season with salt.

Let stand for about 10 minutes, then toss with remaining 1/4 cup vinegar and oregano.

Set aside for another 30 minutes.

Discard bay leaves, then serve warm pork with pickled onions.