Place rice in a fine mesh strainer and rinse under cold water until water runs clear. Tap the bottom of the strainer until well drained.

Transfer rice to a medium saucepan along with 2 1/4 cups water. Bring mixture to a full boil, then reduce heat to low, cover with lid and simmer for 15 minutes. Remove from heat, keep covered and let rest for 10 minutes.

In a small saucepan, combine 4 Tbsp of the vinegar with the sugar and salt. Heat over medium heat, cook and whisk until sugar has dissolved. Remove from heat and let cool while rice is resting, then pour vinegar mixture over rice and toss to coat.

In a small mixing bowl, whisk together mayonnaise and sriracha. Transfer to a sandwich size resealable bag. Set aside.

In a small mixing bowl, whisk together soy sauce and remaining 1 Tbsp vinegar. Set aside.

In a large mixing bowl, gently toss together crab meat, cucumber, carrots, nori, ginger and avocado, or keep it separate and divide chopped ingredients into sections over a rice layer in serving bowls.

Divide prepared rice among 4 or 5 bowls. Top with crab mixture.

Spoon soy sauce mixture over each serving. Cut a small tip from one corner of the resealable bag and drizzle sriracha mayo over each serving. Serve shortly after preparing.