On 4 large buttered squares of heavy-duty aluminum foil, place equal amounts of fish. In small saucepan, melt margarine; add lemnon juice, parsley, dill weed, salt and pepper. Pour equal amounts over fish. Sprinkle with paprika; top with onion slices. Wrap foil securely around fish, leaving space for fish to expand. Grill 5 to 7 minutes on each side or until fish flakes with fork. Refrigerate leftovers.