Butterfly pork tenderloins by splitting each horizontally in half, leaving 1/4 inch intact along other long side. Open up like a book and pound to flatten slightly. Set aside.
Transfer to bowl and add bread crumbs, parsley and sage. Season with salt and pepper to taste, mix well. Spread stuffing over tenderloins, leaving border all around. Fold each in half lengthwise and secure with greased skewers.
In a small bowl, whisk together oil and apple cider for basting. Cook tenderloins on greased grill over hot coals or on medium-high setting, turning and brushing occasionally with cider mixture, for 30 minutes or until pork is no longer pink inside.