Prepare your rice according to the package instructions. Rinse 2-3 times then add water. I use my rice cooker, but you could also make rice in a steamer or on the stovetop.
Deseed the kabocha, peel the skin, and then cut into bite-size pieces.
Bake the kabocha in the oven at 400F for 30 minutes or until tender. I baked mine on a well seasoned cast iron pan, but you could also use a silpat mat on a baking sheet.
Cut the nori into strips that will fit around your rice balls, I use the onigiri mold as a guide.
Using an onigiri mold, fill halfway with the cooked sushi rice and add a piece of kabocha in the center and a tsp of miso paste. Top with more rice then close the mold and press gently.
Flip and release the onigiri, wrap with a piece of nori. Serve & enjoy!