Rinse the sushi rice under cold water until the water runs clear. Drain well.

In a medium saucepan, combine the rinsed rice and water. Bring to a boil over medium-high heat, then reduce the heat to low, cover, and simmer for 20 minutes or until the rice is tender and the water is absorbed.

While the rice is cooking, mix the rice vinegar, sugar, and salt in a small bowl until dissolved.

Once the rice is cooked, remove it from heat and let it sit, covered, for 10 minutes. Then, transfer the rice to a large bowl and gently fold in the vinegar mixture. Allow the rice to cool to room temperature.

Once the rice is cool, wet your hands with water to prevent sticking. Take a small handful of rice (about 1/4 cup) and flatten it in your palm. Place a small amount of diced avocado, cucumber, and shredded crab meat in the center.

Carefully mold the rice around the filling to form a ball. Repeat with the remaining rice and fillings.

If desired, sprinkle sesame seeds on top of the sushi balls or serve with nori strips for wrapping.

Serve immediately with soy sauce for dipping or refrigerate for up to 1 hour before serving.