Combine the rice and water in a saucepan and cook until tender and fluffy.

Transfer the cooked rice to a bowl and gently mix in rice vinegar, sugar, and salt while the rice is still warm.

Press the seasoned rice firmly into a parchment-lined baking dish, creating an even compact layer.

Chill the rice in the refrigerator until completely cold and firm so it can be cut cleanly.

Remove the chilled rice block and slice it into small rectangles or squares.

Heat a thin layer of oil in a skillet over medium heat and fry the rice pieces until the bottoms turn crisp and golden.

Flip and cook the other side until both sides have a crunchy crust.

Place the crispy rice on paper towels or a rack to remove excess oil.

In a mixing bowl, combine chopped tuna, mayonnaise, sriracha, soy sauce, sesame oil, and lime juice until creamy and evenly coated.

Top each crispy rice piece with a slice of avocado and a spoonful of spicy tuna mixture.

Garnish with sesame seeds and chopped green onions before serving.