Heat the oil in a large skillet over medium-high heat. Season the pork tenderloin with salt and pepper, and brown on all sides, about 5-6 minutes total. Transfer the pork to a lightly greased, 6-quart slow cooker.

Add the cranberries, raisins, orange juice, honey and garlic to the slow cooker. Cover and cook on low for about 3 hours, or until a thermometer reads 145 degrees. Remove pork to a cutting board and let stand 10 minutes.

Meanwhile, strain the liquid from the slow cooker through a fine mesh strainer into a medium saucepan, reserving the cranberries and raisins. Whisk together the water and cornstarch in a small bowl, then whisk into the liquid from the slow cooker.

Bring the liquid to a boil over high heat, whisking constantly, until thickened. Stir in the reserved cranberries and raisins. Season to taste with salt and pepper.

Serve the pork with the sauce, and fresh parsley and orange slices to garnish, if desired.