Combine hoisin sauce, honey, sherry and sesame oil in a small saucepan. Bring to a boil, stirring constantly. Reduce heat to low and cook until slightly thickened, about 2 to 3 minutes. Remove from heat and cool. Remove ⅓ of the sauce and set aside.
Trim pork tenderloins of all fat and silverskin. Butterfly the pork by cutting down the center lengthwise to within ¾-inch of the bottom. Press pork open and flatten. Brush all over with ⅓ of the sauce. Cover and refrigerate to let marinate for 4 to 6 hours.
Preheat the grill, and make sure it is well greased. Remove the pork from refrigerator and let stand 15 minutes at room temperature. Grill about 6 minutes per side, or until internal temperature reaches 145℉. Let pork stand 5 minutes while reheating the leftover sauce. Serve the pork drizzled with the remaining sauce and sprinkle with cilantro.
Notes
*To bake this tenderloin, 375℉ for 25 to 30 minutes. Brush 1/2 of marinade on top in beginning and 1/2 on top when you take it out.
*Use peanut or vegetable oil on the grill only- not cooking spray. You'll have better success with not burning your meats.
*If you are preparing this recipe as GLUTEN-FREE, just be sure to use a brand of hoisin sauce that is known to be GF.