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! :-)
Bento is not only rice, but also other ingredients, like... pasta. This recipe came to life when I had some uncooked beef left-overs and just wondered what to do with them. Cooking them as a part of bento was a great idea!
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!