Other types of shredded cheese work great: Cheddar, Monterey Jack, etc.
Frozen chopped kale is a great substitute for the spinach.
If your spinach is frozen into large chunks, place them in a bowl and microwave briefly to thaw. Squeeze out the excess liquid before adding to the baking dish.
The cooking time as specified works perfectly for an 8x8 (one quart) shallow baking dish. I have also used an oval baking dish. This made the casserole a little deeper, and it needed an additional 5 minutes of cooking time to cook through.
Nutrition values are estimates only, using online calculators. Please verify using your own data.