Place pork tenderloins in resealable plastic bag; set aside. In small bowl, combine marinade ingredients; pour over pork. Seal bag; refrigerate for at least 1 hour to marinate, or up to 24 hours to enhance flavor.
Preheat grill to medium-hot. When ready to grill, remove pork from marinade and place on grill. Cook, covered, for about 10 minutes per side (about 20 minutes total) or until the internal temperature of pork is 145 degrees Fahrenheit, followed by a 3-minute rest time.
Meanwhile, place the pineapple chunks on the skewer; place on grill during the last 6 minutes of grilling time, turning after 3 minutes. To serve, slice pork into 1/2-inch slices (medallions) and serve with grilled pineapple.