Rinse the sushi rice under cold water until the water runs clear. Cook in a rice cooker or pot with 2½ cups of water for 15-20 minutes.

Transfer the cooked sushi rice to a bowl, cool slightly, and fold in rice vinegar, sugar, and salt. Spread on a baking sheet to cool completely for 30 minutes.

Shape cooled sushi rice into small rectangular blocks, about 2x2x1 inches, ensuring they hold together.

Heat vegetable oil in a skillet over medium-high heat. Fry rice blocks in batches for 3-4 minutes per side until golden brown.

Dice the sushi-grade tuna and mix with soy sauce, sesame oil, and half of the chopped green onions.

Mix mayonnaise with sriracha to create the spicy mayo.

Assemble sushi by placing tuna mixture on a fried rice block, topping with diced avocado and drizzling with spicy mayo. Finish with tobiko, sesame seeds, and green onions.

Serve immediately for optimal crunch. Consider soy sauce on the side for dipping.