This casserole is simple and delicious, and makes a perfect snack during a picnic (bento anyone?)—you should use it as a basic idea for a casserole, since the pasta sauce is the stable and the most important piece of the meal. It's also a very tweak-able recipe! :-)
You can buy thin beaf slices in some grocery shops or butchers. They may be called minute steaks or quick steaks and are a great ingredient that you can use to make a quick donburi (a rice bowl with meat and vegetable toppings). It's so fast to prepare, that you can do everything in the time it takes to cook the rice!