There's a thread going on elsewhere about this, but I wanted to spread the word over here.
If you peel, core, and slice CHAYOTE (aka christophene or merliton), then parboil the slices, you can bake them up like an apple pie and the resemblance is remarkable. But it's a squash, and way way lower in carbs.
The flavor is very mild, so you need to add sourness and of course cinnamon, sweetness, and BUTTER. I discovered tonight that tamarind paste is freakin' perfect for adding tartness and brown color. (I haven't looked up the carb damage for the tamarind paste, though, and suspect it's high.)
Here's a site with some other names and a picture:
http://www.foodsubs.com/Squashsum.html . It's the second one down, the cute one that looks like what happens to a sock puppet when you make a fist.
Helpful hint: the PLU code for chayote is 4761 so if there's no sticker on the chayote and the cashier at your market can't find it on the list, just have him or her punch that in. (This very well may happen; I haven't yet encountered a cashier who knew what the things were!)