to prepare the bell peppers

1. Slice off the tops and pull out the seeds and slice away any white, pithy skin inside. Slice in half, then slice the halves into halves to make a total of 8 pieces. Repeat with the other pepper.
2. Slice away the paper-thin skin on the outside of the pepper slices. Do this by placing the strip so it’s pointing at 1 o’clock away from you, then slide a sharp knife under it so you can slice off the top while also taking off as little of the flesh under the pepper as possible. Repeat with the remaining slices. The pieces don’t have to be uniform.
3. Combine the mirin and rice vinegar in a tupperware or glass container and place the peppers inside, adding a little more mirin or rice vinegar as needed to cover. Just keep a 2:1 ratio of the liquids.
4. Allow the peppers to marinate in the fridge for 2 days. During this time, they will soften.

to make the sushi rice 

1. Place the rice and water into a rice cooker and cook according to the manufacturer instructions. Once done, season with the rice vinegar, sugar and salt and set aside to cool.

to assemble the nigiri sushi

1. Run your hands under cold water, then take out a bit of the rice and mold into a football shape, about the size of your thumb. Rinse your hands each time before you return to the rice. Repeat until you have 16 pieces.
2. Place a strip of the softened, marinated pepper over each piece of rice, garnishing with sliced scallions and sesame seeds as desired. Serve with soy sauce, pickled ginger and wasabi.