Pressed sushi rice gets chilled, cut, and fried until shatter-crisp, then crowned with sashimi-grade tuna in a tangy-creamy, sriracha-spiked sauce. It’s a restaurant-style bite you can batch ahead and finish in minutes.
Rinse sushi rice under cold water until it runs clear. Add to your rice cooker/pot with water per package directions. Lay the rinsed kombu on top. Cook as usual; remove and discard kombu when done.
In a small bowl, combine rice vinegar, sugar, and salt. Microwave a few seconds to dissolve sugar, then stir.
While rice is hot, gently fold in the sushi vinegar.
Line a tray with plastic wrap; spread rice in an even 3/4-inch (2 cm) layer. Cover with another sheet of plastic wrap. Place a second tray on top and weight it to compress. Chill at least 2 hours (overnight best).
Remove plastic. With a wet knife, cut into bite-size rectangles (about 1.5 x 2.5 inches).
Heat neutral oil to ~350°F (175°C). Fry rice pieces in batches without crowding, 1–2 minutes per side, until deep golden and very crisp. Drain on a rack or on a plate lined with paper towel.
In a bowl, combine diced tuna, green onion, ginger, mayonnaise, sriracha, soy sauce, ponzu, and sesame oil. Mix just to coat; keep chilled.
Spoon spicy tuna onto each crispy rice bite. Garnish with sliced serrano and chopped chives. Serve immediately while the rice is hot and crisp.