Recipe video

Minimum ingredients:

• Onigiri mold (optional if you don't care about the shape of your rice ball)
• Rice
• Any leftovers you have in your fridge
• Seaweed paper, available at your local Asian grocery store (optional)

As far as preparing the leftovers, you do not necessarily need to heat them up if you are making the onigiri with warm rice. I would recommend lightly chopping up the leftovers so you don't end up pulling out a giant piece of meat in one bite.

Here's the one I used from Amazon.