A boneless pork loin roast is the center loin roast with the ribs and T-bones removed. It's important to use the meat thermometer when determining when pork is cooked. Take the meat from the grill when the thermometer registers 150° to 155°F and then let it rest for a few minutes. The temperature will rise to 160°F during resting. This avoids the possibility of overcooking.
Combine the orange juice, juice concentrate, honey, soy sauce, oil, garlic, ginger, five-spice powder, chili paste, and chili oil in a bowl, stirring well.
Put the roast in a shallow glass or ceramic dish and pour the marinade over it. Turn to coat. Cover and refrigerate for at least 2 hours and as long as 12 hours.
Prepare a charcoal or gas grill. Lightly spray the grill rack with vegetable oil cooking spray. The coals should be moderately hot.
Lift the roast from the marinade, reserving the marinade and brushing it on the roast 2 or 3 times during the first 30 minutes of cooking. Grill over indirect heat with the grill covered for about 1 hour and 10 minutes or until a meat thermometer inserted in the center of the roast registers 150° to 155°F. Remove the roast from the grill and let it rest for about 10 minutes before slicing.