1. Heat the coals on a grill to medium hot. In a small mixing bowl, stir together soy sauce, molasses and pepper.
2. Place tenderloin in a shallow dish and pour molasses mixture over. Massage in with hands.
3. Place tenderloin on the hot grill and grill approximately 7-10 minutes. Turning once. Remove from heat and allow to rest for 5 minutes before slicing.
4. To assemble, stuff pita bread with sliced tenderloin, red onion, blue cheese and arugula.
5. Place back on the grill for just a minute to melt cheese.