Cook sushi rice according to package instructions until tender, about 18-20 minutes. Fold in rice vinegar, sugar, and salt.

Line an 8x8 inch baking pan with plastic wrap and pack the seasoned rice mixture into the pan. Refrigerate for at least 2 hours.

Slice the chilled rice into small rectangles, approximately 1x2 inches, for crispiness.

Combine minced tuna, Kewpie mayonnaise, sriracha, sesame oil, and green onions in a bowl. Mix until creamy.

Heat vegetable oil in a skillet to 350°F. Gently fry the rice rectangles in batches for 3-4 minutes on each side until golden brown.

Drain fried rice cakes on a wire rack. Top each cake with the spicy tuna mixture and garnish with jalapeño.

Serve immediately for the best flavor.