In shallow glass or nonmetal container or large reseable food-storage plastic bag, place pork. Pour dressing over pork; turn to coat. Cover container or seal bag; refrigerate 1 to 2 hours to marinate.
Heat gas or charcoal grill. When grill is heated, remove pork from marinade; reserve marinade. Sprinkle pork with garlic powder and pepper; place on gas grill over medium heat or on charcoal grill over medium coals. Add bell peppers to marinade; turn to coat, then place on grill. Cover grill.
Cook pork and peppers 20 to 25 minutes, turning occasionally and brushing with marinade occasionally up to last 5 minutes of grilling, until pork has slight blush of pink in center and meat thermometer inserted in center reads 160°F (if peppers begin to overcook, remove from grill). Discard any remaining marinade.
Cut pepper halves into lengthwise strips; cut pork into slices. Serve pork with peppers.