In a large measuring cup, whisk together vinegar, oil, garlic powder, onion powder, salt, pepper, and honey.
½ cup balsamic vinegar, ½ cup olive oil, 1 teaspoon garlic powder, ½ teaspoon onion powder, ½ teaspoon salt, ¼ teaspoon pepper, ¼ cup honey
Place pork in a zip-top plastic bag and add about ¾ cup of the marinade (set aside the remaining ½ cup of marinade for basting later). Seal the bag and refrigerate at least 2 hours (or up to overnight). Turn the roast over occasionally (if possible), so that it can marinate evenly.
1.5-2 lbs. boneless pork loin roast
Grill, covered, over indirect medium heat for 35-45 minutes or until a meat thermometer reads 145°, basting regularly with remaining marinade. Let stand for 10 minutes before slicing.
Alternative method: Preheat oven to 350 degrees F. Place marinated pork in a large baking dish and pour in the marinade. Roast pork (basting every 10-20 minutes), until a thermometer inserted into center reads 145 degrees F. Let stand for 10 minutes before slicing.