Begin by slicing three different colored bell peppers lengthways using a chopping knife. Thinly slice each segment, then dice into small cubes. Repeat for the avocado.
Prepare the filet of fish by first cutting the filet into a rough rectangle, then slicing lengthways. Dice the fish into cubes approximately 0.5 cm in length and thickness.
For the Nori, you will first need to roll up the sheet and flatten it, pressing along both sides to create a seam. Begin slicing thin strips across the width of the folded sheet, continuing until you reach the end.
Finally, you will need to pre-cook 120g of white sushi rice.
Combine approximately half of the ingredients in a large glass mixing bowl, including your choice of fish (tuna or salmon). Mix well using a wooden spoon.
Further add 120g of the cooked white sushi rice, along with the Nori, and stir until the ingredients are well combined.
Next, take a square of cling-film and place a small ball of the mixture at the center. Bring up the corners of the cling film, then begin to twist it from the top of the ball upward. This will compact the ingredients, forcing them to stick together. Gently squeeze out any pockets of air, and unravel the ball.
Pour a generous helping of black or white toasted sesame seeds onto a flat plate. Using your fingers, gently roll each ball around the plate, ensuring even coverage. The moisture of the rice will help the seeds to adhere to each ball. Repeat this process for each of the sushi balls.
Serve on a wooden sushi board with a small ramekin of Soy Sauce.
Note: To vary the look of your sushi balls, you can use alternative ingredients for the coatings, such as panco or Masago fish roe.