Heat vegetable oil in a pot over high heat until it's very hot. Add the pork cubes, leaving space between the cubes and in a single layer. Sear pork for three to five minutes, turning with tongs to brown on the other side. Work in batches until all pork is browned.
With all the browned pork in the pan, add onion and ½ teaspoon salt. Cook until onions are soft and translucent, about three to five minutes, Add oregano, cumin, coriander, and cayenne. Stir and cook until seasonings get fragrant then reduce the heat to low.
Remove the paper husk from all of the tomatillos. Rinse any sticky residue from the tomatillos and cut into quarters. Into the blender or food processor add garlic, jalapeno, poblano, cilantro, and chicken broth. Pulse on and off until pieces start to break down and you can blend until liquified.
Add browned meat, blended vegetables, 1 teaspoon salt and bay leaf. Cover and turn cooker to high.
Cook 1 ½ hours (maintaining a slow, steady simmer) If you are using potatoes, add them with ½ teaspoon salt, and black pepper. If the mix has reduced where the stock doesn't cover the potatoes, add enough to cover. (As always with a slow cooker, remove the top for only enough time to add ingredients. It takes a while to come back up to temperature.)
Simmer until meat and potatoes are tender, about another 1 ½ - 2 hours.
