How to Make It
In a large bowl, cover beans with cool water, then cover and soak overnight. (Alternatively, place beans in a large bowl and pour boiling water over them to cover, then soak for 1 hour.) Drain.
In a large slow cooker, whisk together tomato paste, broth, 1 Tbsp. zest, juice, cumin, oregano, red pepper and garlic. Stir in beans and onion.
Sprinkle pork with salt. Warm oil in a large skillet over medium-high heat. Cook pork, turning with tongs, until brown on all sides, 8 to 10 minutes. Place pork on top of bean mixture in slow cooker. Cover and cook on low until beans are tender and pork is cooked through and easily shredded, 6 to 7 hours. Taste and adjust seasonings, if desired. Shred pork and stir into bean mixture along with remaining 2 tsp. zest. Serve with rice, sour cream and lime wedges, if desired.