Shirataki noodles are extremely low calorie. So that's one option. Typically you have to go to an asian market for those. They're similar in texture to lo mein noodles.

If you're wanting something with a little more than just carbs to it, check out the pasta aisle at your grocery store. I'm sure there'll be a few different brands of 'protein' pastas. I've had a few different kinds of those, and IMO, as long as you've got something else to help flavor them, they taste pretty good. So they should work well in a casserole.

And there's always the 'No Yolks' egg noodles. Low fat, but it's still the same carb count as a regular pasta/egg noodle.