Sauté sliced mushrooms and green onions in butter in large skillet until just tender; drain. Stir in parsley and set aside.
Trim excess fat from beef tenderloin. cut tenderloin lengthwise to within 1/4-inch of other edge, leaving one long side connected. Sprinkle with seasoned salt and lemon-pepper seasoning. Spoon mushroom mixture onto opening of tenderloin; sprinkle with blue cheese. Fold top side over stuffing. Tie tenderloin securely with heavy string at 2-inch intervals. Place tenderloin in a large, shallow dish. Pour dressing over tenderloin; cover and refrigerate 8 hours or overnight, basing with marinade occasionally.
Remove tenderloin from marinade. Press crushed peppercorns onto each side of tenderloin. Bake at 350° F for 40 minutes or grill over medium-hot coals, covered or tented, 35 minutes or until meat thermometer registers 140° F (60*C) for rare, 160° F (70*C) for medium. Transfer to platter, remove string and slice to serve.Servings: 4