Mix together mustard, vinegar, oilive oil, pineapple juice, tarragon and pepper. Simmer in a saucepan until evenly heated. Keep Sauce Warm.
Preheat grill.
Lightly pound filets with kitchen mallet and sprinkle with salt and pepper. Place filets on the grill and cook about 4 minutes on each side or until desired donesness is achieved. Remove filets from grill.
Place about 2 Tbsp. of mustard mixture on a plate and place filet on top of sauce. Serve Immediately.