In a 4- to 6-quart slow cooker, combine the salsa, chili powder, oregano, cocoa, and 1 teaspoon salt. Add the pork and turn to coat.
Cook, covered, until the meat is tender and pulls apart easily, on high for 4 to 5 hours or on low for 7 to 8 hours.
Twenty minutes before serving, heat oven to 350° F.
Stack the tortillas, wrap them in foil, and bake until warm, about 15 minutes.
Meanwhile, using 2 forks, shred the pork and stir into the cooking liquid. Serve with the tortillas, cilantro, sour cream, lime, and extra salsa.