(Depending on the depth of your 9x13 pan, you may need to make two casseroles. I have noticed that if I use disposable aluminum pans- I usually have to divide this casserole into two pans)
You can substitute the loaf of gluten free bread with a loaf of french bread as well.
I've even gone as far as using up WHATEVER bread I have in the house that needs to be used up. I've even cut up dinner rolls and one time I had one piece of naan bread that made it in there too!