There are already several mini-burger or tsukune dumpling type of recipes here, but here's another one. What can I say - mini-burgers are just perfect for bentos: they taste good when they are cold, can be made in quantity, and usually freeze very well.
This time it's a shrimp and tofu version, adapted quite a bit from a recipe in a recent issue of Kyou no ryouri: Beginners (Today's Cooking: Beginners) magazine. It's best when made with fresh shrimp, but uncooked frozen shrimp is fine. You probably don't want to be messing around with shrimp paste in the morning, so it can made it the night before (have some for dinner too - it's great hot) or freeze a batch. The sweet-hot red pepper jam I've used as a sauce goes very well with it, but if you don't want to go to the trouble of making the jam, use a sweet or hot bottled chili sauce.