Ok...probably not the healthiest...but we found it yummy on our fish a few weeks ago (found it on a website....we used it on smoked cod though - but sure it would go with most other fish i'm no cook)

Its a creamy parsley sauce:-

Ingredients
¼ cup fresh parsley chopped
1 tablespoon margarine
1 tablespoon plain flour
½ - ¾ cup milk
a squeeze lemon juice
salt and pepper

To make the sauce; melt the margarine, then add the flour to make a thick paste. You may need to add a little more if needed. Add the milk to make a sauce, stirring as much as you can to reduce lumps. Again, the milk quantity may vary depending how much flour was used. Keep stirring and once you get the consistency you like, add in the parsley, salt and pepper and the lemon juice and keep stirring.