Drain the pineapple reserving 1/4 cup of juice. Combine the pineapple juice, the salad dressing, tomato sauce, sugar and mustard in a shallow dish. Mix well. Add the shrimp, tossing gently to coat. Cover and marinate in the refrigerator for 2 hours, stirring occasionally.
Remove the shrimp from the marinade, reserving the marinade. Alternate shrimp, pineapple and green pepper on 4 skewers. Grill over medium hot coals 3-4 minutes on each side or until done, basting with the marinade.
Heat the reserved marinade and place it in a bowl for serving.