Mix the first 10 ingredients together.
Stuff the seafood filling into the cooled manicotti and set the manicotti into a greased 8 by 8 inch pan.
In a medium heavy saucepan, melt the butter on low/medium heat.
Whisk the flour into the butter.
Slowly pour in the milk, whisking continuously. Heat until thickened. Do not boil.
Add the parmesan cheese and stir.
Pour the sauce over the stuffed manicotti.
Put into 350 degree preheated oven and bake for 20-30 minutes or until hot and bubbly.
Top with chopped green onions.