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.
Tip: When using a slow cooker, resist the urge to lift the lid until the dish has cooked the minimum amount of time specified in the recipe. Each peek allows heat to escape and can increase cooking time by as much as a half hour.