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!
Today was one of these days that my coffee needed a coffee... And I really couldn't make myself cook in the morning. So, the vegetarian bento was made! It's fast, it's simple, and it tasted great. Consider that a fancy salad for lazy days.