Preheat one barbecue burner to medium heat and leave other burner off. Brush grill with oil. Grill pork 8 minutes, turning once. Transfer pork to cool side. Grill, lid down, and adjust hot burner if necessary to maintain temperature of 375°F (190°C) for 30 to 40 minutes or until cooked through. Transfer to cutting board; cover loosely with foil. Let stand 10 minutes. Cut into ¼-inch (5 mm) thick slices.
Meanwhile, whisk together garlic, miso paste, vinegar, maple syrup, mustard and pepper in large bowl. Gradually whisk in oil. Add green onions, carrots, celery, apples and cabbage; toss to coat.
Servepork with cabbage mixture. Sprinkle with chives (if using).