In a medium bowl, combine the soy, rice wine vinegar, chili sauce, ginger, garlic, scallions and orange zest. Place the pork in a large container or bowl and pour the marinade over the pork. Cover with plastic wrap, and let sit for 2 hours at room temperature, or overnight in the refrigerator.
Remove the pork from the container, put the marinade in a small saucepan and bring it to a boil over medium heat. Remove from the heat and reserve it for drizzling over the pork when serving. *WARNING: This liquid MUST be brought to a boil to kill any bacteria from raw meat juices.
Preheat the grill to medium-high heat.
Dust the pork liberally with the ground coriander seed and place on the preheated grill. Brown it on all sides then move it to a cooler part of the grill to cook it to desired doneness, about 10 to 12 minutes.
Remove the pork from the grill to a cutting board and let rest for 10 minutes before slicing. Slice the pork on the bias and place on a serving platter. Serve drizzled with the reserved boiled soy marinade.