Breakfast casserole can be part of a healthy diet, it all comes down to what ingredients you add to the casserole. The basis for most breakfast casseroles is eggs, seasoning, and a liquid such as milk, cream, or plant based milks. Some casseroles might be filled with lots of cheese, high fat meats, and hashbrowns, but you can also just as easily make a healthy breakfast casserole filled with lots of vegetables. It's also easy to make it meatless or use lean meats, or to skip the cheese.