1. Place tenderloin in a large resealable plastic bag. Whisk together the vinaigrette and cumin in a measuring cup. Pour 1/2 cup of the dressing into bag with pork. Let marinate at room temperature while heating grill.
2. Heat grill to medium-high or medium-hot coals. Once hot, remove pork from marinade and grill for 18 minutes, turning frequently, until it registers 140 degrees on an instant-read thermometer. Remove to a cutting board, tent with foil and let rest 5 minutes.Black Bean Salsa:
3. Meanwhile, in a small bowl, stir together the black beans, pineapple, red pepper, salt, pepper and remaining 1/4 cup cumin-dressing mixture. Slice pork on a slight diagonal into 1/4-inch-thick slices. Serve with salsa alongside.