Tuna paste is ridiculously easy to prepare and makes a great no cooking bento, cutting the preparation time to less than 20 minutes, including rice cooking time! Now, that's what I would call cooking on the go! You can also use the tuna paste for a great tasting onigiri or sushi.
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!