Rinse sushi rice until water runs clear. Cook in a rice cooker or stovetop according to package directions.

Mix rice vinegar, sugar, and salt. Fold into the hot cooked rice gently.

Line an 8x8 inch pan with plastic wrap. Press rice firmly into the pan to create an even layer. Cover and refrigerate for at least 2 hours (or overnight).

Remove chilled rice block and cut into uniform rectangles (approx 2x1 inches).

Heat vegetable oil in a skillet over medium-high heat. Fry rice cakes for 3-4 minutes per side until golden brown and crispy. Drain on wire rack.

In a bowl, mix diced tuna, mayo, sriracha, sesame oil, soy sauce, and chopped scallions.

Assemble by placing a slice of avocado on the crispy rice, topping with a spoonful of spicy tuna, and garnishing with a jalapeno slice and sesame seeds.

Serve immediately while rice is warm and crispy.