Rinse sushi rice under cold water until it runs clear. Combine with water in a medium saucepan, bring to a boil, reduce heat to low, cover, and simmer for 18-20 minutes. Allow to rest for 10 minutes.

In a small saucepan, combine rice vinegar, sugar, and salt. Heat over low flame until sugar dissolves. Set aside.

Mix sushi rice with prepared seasoning gently. Press into an 8x8 pan lined with plastic wrap, cover, and chill for at least 30 minutes.

Cut the chilled rice into rectangles measuring 2 inches by 1 inch, making about 15 pieces.

Heat vegetable oil in a deep skillet to 350°F. Add rice rectangles in batches and fry for 2-3 minutes per side until golden brown. Drain on paper towel.

Combine chopped tuna with Kewpie mayonnaise, Sriracha, soy sauce, and lime juice in a bowl. Mix until well-coated.

Slice avocado into wedges and dice jalapeños if using. Prepare toppings for assembly.

Assemble by placing a slice of avocado on each piece of crispy rice, followed by spicy tuna mixture, jalapeños, and sesame seeds. Serve immediately.