Slice the tuna and salmon very thinly on the bias, with pieces about 2 inches long.

Slice the cucumber in half and then again in half lengthwise. Using a mandolin on a very thin setting, slice the cucumbers into spears, lengthwise. Cut them into 2 inch pieces. Slice the radishes on the mandolin.

Working around the donut mold in batches, press the fish into the bottom of the donut mold, then the cucumbers, then the radishes, spoon in the salmon roe, and sprinkle in the sesame seeds.

Repeat with each mold. Press in the rice on top of the other ingredients, making the top of the rice as flat as possible. Place the mold in the refrigerator for at least 5 minutes.

Remove from the refrigerator, place a flat plate or tray on top of the mold and flip over the mold. Carefully remove the mold from the donuts.

Top the donuts with slices of chives and serve with soy sauce or Ponzu sauce, pickled ginger, and wasabi paste.

Thoroughly rinse 1½ cups of sushi rice until water is clear. Place in a rice cooker, along with 2 cups water. Cook until button pops up.

In a small sauce pot, combine 3 tablespoons rice vinegar, 2 tablespoons sugar, and 1 teaspoon salt. Dissolve over medium heat but do not boil. Remove from heat and stir. Set aside to cool.

Once rice is finished, let sit in the steamer for 5 minutes.

Remove rice and place into a wooden or non-reactive bowl. Fold in the vinegar mixture gently. Let rice cool to room temperature before handling.