In a bowl, stir together the brown sugar, five spice blend, minced garlic, rice vinegar, soy sauce, and 1/2 cup water.
Trim the fat from the pork loin if desired, then cut the meat into 3-inch chunks. Place the meat in the bottom of a 4-quart or larger slow cooker. Pour the spice mixture over the meat.
Place the lid on the slow cooker and cook on high for 4-5 hours or low for 8-10 hours.
After cooking the meat should be fall-apart tender. Carefully remove the chunks of meat from the slow cooker with tongs. Remove any large pieces of fat or gristle, then shred the meat with two forks.
Remove any pieces of fat or debris from the liquid in the slow cooker. In a small bowl stir together 1 Tbsp cornstarch and 2 Tbsp water. Pour the cornstarch mixture into the liquid in the slow cooker and stir to combine. Return the shredded meat to the cooker and stir to coat in the liquid. Replace the lid and cook on high for 30 more minutes, or just until the liquid begins to bubble and thicken. Serve hot.
*This spice blend is also called Chinese Five Spice and is a blend of aromatic spices like anise, cinnamon, cloves, and pepper. If you can't find it in the regular baking and spice aisle, check the international foods section of your grocery store.