Rinse the sushi rice under cold water until the water runs clear. Drain well and cook with 2 1/4 cups water in a rice cooker or pot.

In a small saucepan, heat rice vinegar, sugar, and salt until dissolved. Let cool slightly.

Transfer the cooked rice to a large bowl. Gently fold in the vinegar mixture while fanning the rice to cool it down.

Beat the eggs with soy sauce and mirin. Cook into a thin omelet, then slice into thin strips.

Slice the cucumber, avocado, and sashimi into thin, bite-sized pieces.

Divide the sushi rice among bowls. Arrange the sashimi, cucumber, avocado, and egg strips on top.

Garnish with shredded nori, sesame seeds, pickled ginger, and wasabi if desired.