Gadwall eat just like any other duck. I have a great number of duck recipes here
, for starters. If your gadwall are fat, you have no problems. If they are skinny, however, you can either lay thick bacon strips over the breast as you roast them or slip butter or duck fat under the skin of the breasts to keep them tender.
If you have breasted them out, they're no different from anything else, so you can follow some of my recipes or any of the other good ones on this forum. Enjoy!
I love all of God's creatures, properly prepared.