For sauce, in a bowl combine coconut milk, basil, mint, onions, lime peel and juice, fish sauce, brown sugar, curry paste, 1 teaspoon coarse salt, and 1/2 teaspoon ground black pepper. Set aside. For rub, in a bowl combine ginger, garlic, salt, and 1 teaspoon ground black pepper. Untie and unroll lamb. Trim fat. Using flat side of meat mallet, pound lamb to an even thickness (1-1/2 to 2 inches thick). Rub ginger mixture over lamb. Place in large sealable plastic bag set in shallow dish. Add 1/2 cup of the sauce. Seal bag; turn to coat. Refrigerate overnight. Cover and refrigerate remaining sauce.
Remove meat from marinade. To keep meat from curling, insert 2 long metal skewers through meat forming an X. To grill, arrange medium coals around drip pan. Test for medium-low heat above pan. Place meat on rack over pan. Cover; grill 50 to 60 minutes or until instant-read thermometer registers 135 degree F for medium-rare. Let chilled sauce stand at room temperature 30 minutes. Remove meat. Cover with foil; let stand 15 minutes. (Temperature will rise 10 degrees.) Thinly slice meat against grain; serve with sauce. Makes 8 to 10 servings.