Rinse the sushi rice under cold water until the water runs clear, then drain.
In a medium saucepan, combine the rinsed sushi rice and water. Bring to a boil over medium-high heat.
Once boiling, reduce the heat to low and cover the saucepan. Cook for 18-20 minutes, or until the rice is tender and the water is absorbed.
While the rice is cooking, make the sushi vinegar mixture by combining rice vinegar, sugar, and salt in a small bowl. Stir until dissolved.
After the rice is cooked, remove it from heat and let it sit covered for 10 minutes. Then transfer the rice to a large bowl. Pour the sushi vinegar mixture over the warm rice and gently fold it with a wooden spoon or spatula. Allow the rice to cool to room temperature.
In a small bowl, combine the diced tuna with mayonnaise and sriracha. Mix well to coat the tuna.
To assemble the sushi bowl, place a scoop of warm sushi rice at the bottom of a bowl.
Top with the spicy tuna mixture, avocado slices, cucumber, edamame, and a sprinkle of sesame seeds.
Garnish with chopped green onions and, if desired, strips of seaweed. Drizzle with soy sauce for added flavor.
Notes
Serve in deep bowls for a layered effect. Arrange the toppings artfully for a colorful appearance.