In a measuring cup, whisk the coconut milk, peanut butter, soy sauce, lime juice, brown sugar, garlic, and coriander to make the peanut sauce.
Trim the pork of excess fat and remove the silver skin - click up above for instructions. Butterfly the tenderloin by splitting it lengthwise almost but not quite all the way through, so the halves remain attached.
Open the tenderloin (like a book) then cover with saran wrap, and pound to a 1/2-inch thickness with a meat mallet. Put the pork tenderloin in a large zip lock bag then pour half the marinade on top (reserving the other half). Squish it around so the meat is evenly coated. Place the meat in the refrigerator and marinate for 4 hours. Remove from the refrigerator 20 minutes prior to cooking to let the meat come to room temperature.
Heat a large grill pan coated in cooking spray over medium high heat. Remove the tenderloin from the marinade then lightly season both sides with sea salt and freshly cracked pepper, to taste. Place the tenderloin in the HOT grill pan then cook for 5 -6 minutes before flipping and cooking for an additional 3-4 minutes, or until the pork is cooked through. Transfer to a carving board and let the meat rest for 5 minutes before slicing and serving the the reserved peanut sauce on the side (I heated the sauce up for 20-30 seconds in the microwave before serving). Enjoy.