- Make the barbecue sauce by heating tomato sauce, teriyaki sauce, brown sugar, five spice, garlic, and cayenne in a small saucepan over medium heat until it reaches a low boil. Stir and reduce heat to simmer. Simmer 5 minutes. Turn heat off and pour barbecue sauce into a small jar, setting aside 1/4 cup for basting pork.
- Heat a cast iron grill pan or an outdoor grill over medium-high heat and grease with oil. In the meantime, pat pork tenderloin dry with paper towel to remove excess moisture. Place pork on hot pan and grill for 10 minutes. Turn pork and baste with a couple tablespoons of reserved barbecue sauce. Grill 10 minutes longer. Turn pork once more and baste opposite side with barbecue sauce. Cook 3 minutes longer. Serve hot with extra barbecue sauce.