Follow these steps to create your Spicy Shrimp Sushi Stacks:

1. Cook the Sushi Rice: Rinse the sushi rice under cold water until the water runs clear. Combine the rice and water in a pot, bring to a boil, then reduce heat, cover, and simmer for 20 minutes. Remove from heat and let it sit, covered, for an additional 10 minutes.

2. Prepare the Sauce: In a small bowl, mix the mayonnaise and Sriracha until well combined. Adjust the heat level based on your preference.

3. Season the Rice: In a separate bowl, mix the rice vinegar, sugar, and a pinch of salt until the sugar dissolves. Stir this mixture into the cooked rice, gently folding it to avoid mashing the grains.

4. Cook the Shrimp: In a skillet over medium heat, add sesame oil. Cook the shrimp for about 2-3 minutes on each side until they are pink and opaque.

5. Prepare the Vegetables: Slice the avocado and julienne the cucumber. Chop the green onions for garnishing.

6. Assemble the Stacks: Take a small round mold or a cup, and layer the sushi rice, shrimp, avocado, and cucumber inside. Press down lightly to compact the layers.

7. Remove the Mold: Carefully remove the mold to reveal the stacked ingredients.

8. Garnish and Serve: Drizzle with soy sauce and top with green onions, sesame seeds, and a dollop of the spicy mayo.