In a medium skillet heat oil over a medium-high heat. Chop scallions and add white parts to skillet, reserving green parts. Add garlic and ginger.
Stirring, cook until vegetables start to soften. Add Fish Sauce, Curry Paste and brown sugar. Stirring, cook until curry is dissolved and fragrant. Cool ingredients.
Add 1/2 cup mint (reserving remains for garnish) and 1/4 cup of lime juice to curry mixture. Stir well and pour into zip lock gallon size plastic bag.
With a sharp knife, butterfly pork by slicing lengthwise down center, cutting three quarters of the way through meat. Open like a book. Add meat to plastic bag and cover all sides with marinade. Squeeze out air and lay flat in refrigerator. Marinate for one hour.
Preheat grill to medium high and oil grates. Grill 6 minutes per side or until meat registers 150 degrees on a meat thermometer (pork can be slightly pink).
Meanwhile squeeze marinade from plastic bag into a small saucepan. Add remaining 1/4 cup lime juice and bring to a boil. Turn down to a simmer and cook 5 minutes. Strain through a fine sieve and reserve sauce.
Slice tenderloin on a diagonal and pour reserved sauce over meat.
Sprinkle with remaining mint and peanuts.
Jasmine rice and cucumber salad nicely compliment this dish.