Rinse the sushi rice under cold water until the water runs clear. Combine the rice and water in a medium saucepan and bring to a boil. Once boiling, reduce heat to low, cover, and simmer for 18-20 minutes or until the rice is tender and water is absorbed. Remove from heat and let it sit covered for 10 minutes.

In a small bowl, mix rice vinegar, sugar, and salt until dissolved. Fluff the cooked rice with a fork and gently fold in the vinegar mixture. Allow the rice to cool to room temperature.

While the rice cools, heat olive oil in a skillet over medium heat. Season the shrimp with garlic powder, paprika, cayenne pepper, salt, and pepper. Cook the shrimp for 2-3 minutes on each side or until they turn pink and opaque. Remove from heat and let cool slightly.

In a separate bowl, mix mayonnaise and sriracha to create a spicy sauce. Adjust the amount of sriracha to taste.

To assemble the stacks, use a round mold or a small cup. Start with a layer of sushi rice, followed by a layer of sliced avocado, a layer of shrimp, a drizzle of spicy mayo, and a layer of cucumber. Repeat the layers until you reach the top of the mold.

Carefully remove the mold and sprinkle sesame seeds and chopped green onions on top. Serve with nori strips on the side if desired.