Rinse the short‑grain rice under cold water until the water runs clear, then combine with 1½ cups water in a saucepan. Bring to a boil, cover, and reduce to a low simmer for 12 minutes. Remove from heat and let sit, covered, for 10 minutes. Transfer the hot rice to a large bowl, drizzle with ¼ cup rice vinegar, and fold gently with a wooden spoon until evenly coated. This step creates the signature sticky texture essential for stacking.

Mixing the Spicy Tuna

Combine the sauce. In a small bowl whisk together 2 tablespoons Japanese mayo, 1 tablespoon sriracha, 1 teaspoon toasted sesame oil, and 1 teaspoon soy sauce. The mixture should be smooth, glossy, and slightly spicy.
Season the tuna. Add the diced tuna to the sauce, tossing gently to coat each piece. Let the tuna rest for 5 minutes so the flavors meld; the acid from the soy and sesame oil will brighten the fish.
Check consistency. If the mixture feels too thick, stir in a splash of cold water or a few drops of extra soy sauce. The goal is a creamy coating that clings without drowning the tuna.

Building the Stacks

Using a small round mold (or a clean ramekin), place a spoonful of seasoned sushi rice at the bottom of each serving plate and press lightly. Layer a thin slice of avocado, then a generous spoonful of the spicy tuna mixture. Add a few cucumber julienne strips, another small mound of rice, and finish with a final tuna topping. Press gently after each layer to keep the stack stable.

Finishing Touches

Sprinkle chopped scallions and black sesame seeds over the top of each stack. Serve with a side of pickled ginger, a dab of wasabi, and a small dish of soy sauce for dipping. The contrast of warm tuna, cool avocado, and tangy rice makes every bite a delightful adventure.

Tips & Tricks

Perfecting the Recipe

Use truly sushi‑grade tuna. This ensures a buttery texture and safe raw consumption, making the flavor stand out.

Season the rice while hot. Adding the vinegar to warm rice helps the grains absorb flavor evenly.

Chill the tuna mixture. A quick 10‑minute chill in the fridge firms the coating, preventing it from sliding off the stack.

Flavor Enhancements

Finish each stack with a drizzle of freshly squeezed lime juice for bright acidity. Add a pinch of toasted nori flakes for an oceanic umami boost, or stir a teaspoon of miso paste into the mayo for deeper savory notes.

Common Mistakes to Avoid

Avoid over‑mixing the tuna; vigorous stirring can break down the delicate flesh and make the mixture mushy. Also, never use rice that’s too wet—excess moisture will cause the stack to collapse.

Pro Tips

Prep all components ahead. Slice avocado, cucumber, and scallions while the rice cooks to streamline assembly.

Use a silicone mold. It creates uniform, restaurant‑style towers and makes removal effortless.

Adjust heat level. If you prefer milder heat, start with half the sriracha and taste before adding more.

Garnish just before serving. This keeps avocado from browning and preserves the crunch of cucumber.

Variations

Ingredient Swaps

Substitute tuna with diced salmon or cooked shrimp for a different oceanic profile. Swap avocado for ripe mango to introduce a sweet contrast, or replace cucumber with thinly sliced radish for extra peppery bite. If you’re avoiding raw fish, use seared ahi steak diced into bite‑size pieces.