The garlicky, tangy flavor of mojo sauce is used for all types of meat in the Caribbean, but especially for pork in Cuban cooking. For pork roasts, or lechon asada, mojo sauce is commonly used as both a marinade, cooking liquid and dipping sauce. For slow cooking, you'll want to use a pork shoulder cut, such as whole pork shoulder or Boston butt, which becomes extremely tender when cooked in the low heat of your slow cooker. Although you can find prepared mojo sauce in Latin grocery stores, it's easy to whip up a fresh batch at home.
Create the mojo sauce by blending sour orange juice with olive oil, garlic cloves, dried oregano, cumin, kosher salt and freshly ground black pepper in a mixing bowl, using a hand blender. For every 1 cup of mojo sauce, you'll need about 2/3 cup sour orange juice and 1/3 cup olive oil. Blend until smooth. You'll need enough mojo sauce for both marinating and cooking in the slow cooker.
Place your pork roast in a large resealable bag and cover with enough mojo sauce to fully coat the pork. Seal the bag and let the roast marinate in the refrigerator overnight. Reserve the rest of the mojo sauce in a separate container in the refrigerator.
Heat a deep saucepan coated with vegetable oil over high heat. Add the marinated pork roast and sear in the hot oil on all sides, using tongs to carefully lift and turn the roast. Sear until all sides are well browned.
Transfer the pork roast to a slow cooker, along with the reserved mojo sauce. There should be enough mojo sauce to reach halfway up the roast. If there is not, you can add a few more splashes of sour orange juice, chicken broth or water. You can also add sliced onions to the slow cooker before adding the pork roast for more flavor.
Cover the slow cooker and let the pork roast cook on low for 8 to 10 hours. The pork should easily pull apart with a fork when it's ready. If you're not sure, use a meat thermometer to check the temperature. Pork shoulder roasts become extremely tender when the internal temperature reaches around 195 degrees Fahrenheit. Transfer the pork to a platter to let it rest for at least 15 minutes before slicing it, or shredding it for pulled pork.