Rinse sushi rice under cold water until water runs clear. Combine with water in a medium pot. Bring to a boil, reduce to low, cover, and simmer for 15 minutes. Let sit covered for 10 minutes.

Mix rice vinegar, sugar, and salt in a bowl until dissolved. Fold into warm sushi rice gently, keeping it fluffy.

Combine mayonnaise and sriracha in a bowl, whisk until smooth. Adjust spice level as desired.

Chop shrimp into bite-sized pieces and toss with half of the spicy mayo until coated.

Layer sushi stacks in a ring mold: rice, cucumber, avocado, and shrimp. Press gently to hold layers.

Lift ring mold and drizzle remaining mayo on top. Garnish with nori and sesame seeds. Serve immediately.