Rinse 1 cup of sushi rice under cold water until the water runs clear, about 2-3 minutes. Cook according to package directions, 15-20 minutes. Mix cooked rice with 3 tablespoons rice vinegar, 1 tablespoon sugar, and 1 teaspoon salt while warm, then cool to room temperature.

In a separate bowl, combine 1 pound shrimp, 2-3 tablespoons sriracha, and 2 tablespoons mayonnaise. Mix well and let sit for about 10 minutes.

Slice 1 ripe avocado and 1 cucumber into thin rounds. Set aside for layering.

Place a mold on a plate. Layer sushi rice, spicy shrimp, avocado, and cucumber. Repeat until mold is full, pressing down gently.

Carefully lift the mold to reveal stacked sushi. Reshape if needed.

Top with optional nori strips. Serve immediately with soy sauce or extra sriracha.