Make the rice: place the rice in a colander and rinse it with water until it runs clear. Place the drained rice in a saucepan, add the water, and heat over medium-high heat. Bring to a boil and reduce the heat. Simmer, covered, until all the water has been absorbed, about 15 mins. Remove from heat and let it sit, covered for 15 mins.
Mix the rice vinegar, salt, and sugar in a measuring cup. Transfer the cooked rice to a bowl and use a paddle to break it up. Drizzle the prepared vinegar over the rice and mix until the vinegar is well incorporated and the rice has cooled down. Cover with a damp towel until cooled down completely.
Prepare the bowls: divide the rice, surimi, avocado, and cucumber between 5 bowls. Rice first, toppings over rice.
Mix the mayonnaise with the sriracha and drizzle over the bowls. Top with chopped nori and toasted sesame seeds, and serve with pickled ginger and soy sauce on the side.