A quiche is made of a mix of eggs and cream or milk  almond milk for dairy-free) and poured into a pastry crust along with chopped or diced meats and an assortment of chopped or diced veggies. A breakfast casserole, also known as an egg bake, is similar to frittata because it is not baked in a pasty crust. Breakfast casseroles can range quite a bit. In general they contain eggs as well as a  variety of ingredients like vegetables, cheese, and breakfast meats and are baked in a casserole dish.