I have never tried the slow cooker, or even thought about it to be honest. One thing that has worked for me is the "10 minute rule" when baking.
http://orcabayseafoods.com/cooking-r...e-cooking-fish
It has worked great for me and I usually add a few minutes to it. Never cooked anything over 1.5" thick so I don't even bother flipping it.