Just Bento

Hi !
It seems like I must eat more iron-rich foods in order to be able to make my next blood donation... I'd like to eat more kidney products especially, but the only way I ever had kidney was simply pan-fried or pan-seared. I've seen a few recipes suggesting an onion or mushroom based sauce to go with that, but it still does't seem so bento-friendly (the kidneys are still cooked medium-rare).

So, have you any ideas or recipe for kidney that would suit a bento box ?
[EDIT]
Liver recipes are most welcome too ! And offal meat in general in fact... ^^