Use heavy aluminum foil cut into large squares. Place equal portions of the fish fillets on each piece of foil. In a saucepan, melt margarine. Add lemon juice, parsley, dill, salt and pepper. Stir to blend well. Pour this mixture over the fish, sprinkle with paprika, and top with the onion slices which have been separated into rings. Fold the foil around the mixture and seal using a drugstore fold or other method of sealing tightly. Leave a little space for the food to expand while cooking. Place on hot grill and grill for 5-7 minutes per side. Fish should flake easily when done.