Rinse the sushi rice under cold water until the water runs clear.

In a medium saucepan, combine the rinsed rice and water. Bring to a boil, then reduce heat to low, cover, and simmer for 18-20 minutes until the rice is tender.

Remove from heat and let it sit covered for 10 minutes.

In a small bowl, mix the rice vinegar, sugar, and salt until dissolved. Gently fold this mixture into the cooked rice. Allow the rice to cool to room temperature.

In another bowl, combine the mayonnaise and sriracha sauce to create a spicy mayo. Adjust the amount of sriracha to your preferred spice level.

To assemble the stacks, use a round mold or a small cup. Start with a layer of sushi rice, followed by a layer of spicy mayo, then a layer of shrimp, avocado, and cucumber. Repeat the layers until the mold is full.

Carefully remove the mold and sprinkle sesame seeds and sliced green onions on top.

Serve immediately with nori squares on the side for wrapping.