I did a few things differently when I made this: One, I used skim milk instead of evaporated milk. I didn't measure exactly how much I used--I just kept adding it until I had enough of the sauce. I also sauteed mushrooms and added them in with the squash.
This is seriously one of my new favorite dishes, and it was pretty easy over all. Just make sure you get the sauce all the way to the edges of the lasagna noodles or else the edges are crunchy. It's originally a Weight Watchers recipe, FYI.