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Two triangle onigiri wrapped with nori on a plate.

Tuna Mayo Onigiri (Triangle Rice Balls)

Filled with creamy tuna and wrapped in crisp nori, these Tuna Mayo Onigiri (Triangle Rice Balls) are perfect for lunchboxes, picnics, and quick snacks. Portable, satisfying, and surprisingly easy to prepare.

Course: Snack
Cuisine: Japanese
Prep Time: 45 minutes
Cook Time: 12 minutes
Total Time: 57 minutes
Servings: 2
Author: Manuela Zangara

Ingredients

  • 100 g – 3.5 oz sushi rice
  • 1 tsp salt
  • 110 ml – scant ½ cup water
  • 30 g – 2 tbsp canned tuna – drained
  • 1 tbsp Japanese mayo
  • 1½ tsp sesame seeds – toasted
  • Nori strips

Instructions

Preparing the Rice

  1. Wash the rice very well under cold water. Make sure the water runs clear at the end of the wash.
    Sushi rice soaking in a glass bowl of water before cooking.
  2. Place the rice in a large bowl and soak it for 30 minutes.
  3. After 30 minutes, drain the rice and transfer it to a pot. Add the water and salt (if you will be using a mould to shape your onigiri). Cover with a tight-fitting lid and bring to a boil over high heat. Once it starts to boil, reduce the heat to low and simmer for 10 to 12 minutes, or until all the water has been absorbed.
  4. When ready, let the rice rest for 10 minutes before removing the lid.
    Cooking sushi rice in a pot and letting it rest with the lid on to absorb steam.
  5. Add the toasted sesame seeds and mix gently.

Preparing the Filling for Tuna Mayo Onigiri

  1. Mix the drained tuna with the Japanese mayonnaise until well combined.
    Mixing canned tuna with Japanese mayonnaise to make onigiri filling.

Shaping the Onigiri

  1. Let the cooked rice cool slightly until you can hold it comfortably without burning your hands. Do not let it cool completely, or it will become firm and difficult to shape.
  2. To shape the onigiri by hand, wet both hands with water to prevent the rice from sticking.
  3. Sprinkle a little salt on your hands and rub them together to spread it evenly.
  4. Scoop out a handful of warm rice (about ½ cup) into one hand. Using the other hand, make an indentation in the centre and place half of the filling inside. Gently press the filling into the rice.

  5. Shape the rice around the filling to form a triangle. Shape the bottom edge with your left hand and the top corner with your right hand. Use your thumb, index, and middle fingers to guide the corners. Press the triangle lightly between your palms, firm enough so it holds its shape but not so tight that the rice becomes compacted.

    Note: If you are using an onigiri mould, fill it halfway with rice, add the filling in the centre, cover with more rice, and press down to shape. Add 1 teaspoon of salt to the rice when cooking if using a mould.

    Assembling Tuna Mayo Onigiri using a mould and layering rice with tuna filling inside.

  6. Before serving, wrap each onigiri with a strip of nori (seaweed).

    Wrapping triangular onigiri with a strip of nori.