Rinse sushi rice under cold water until clear. Combine rice and water in a medium saucepan, boil, reduce heat, cover, and simmer for 18 minutes. Let sit for 10 minutes off heat.

In a bowl, mix rice vinegar, sugar, and salt. Fold into warm rice gently and let cool.

Slice cucumber into strips and dice avocado. Sprinkle lemon juice on avocado to prevent browning.

Layer rice in bowls, top with cucumber and avocado. Add shredded crab or tofu as protein.

Mix soy sauce and sriracha, drizzle over bowls, and sprinkle with sesame seeds or nori.

Serve immediately with pickled ginger and wasabi if desired.