01 - Combine warm cooked rice with rice vinegar, sugar, and salt in a small bowl. Spread the seasoned rice onto a tray and let it cool completely, or chill uncovered for extra dryness to achieve crispier results.
02 - Moisten your hands and shape the chilled rice into 12 small rectangles or rounds, using about 2 tablespoons each. Gently flatten each piece into ½-inch thick patties.
03 - Heat neutral oil in a nonstick skillet over medium-high heat. Fry the rice pieces for 2–3 minutes per side until golden brown and crispy. Transfer to a paper towel-lined plate and let cool slightly.
04 - Combine drained tuna, mayonnaise, sriracha, soy sauce, chopped green onion, diced avocado, and toasted sesame oil in a mixing bowl. Mix gently and fold in sesame seeds.
05 - Arrange the crispy rice pieces on a serving platter. Top each piece with a generous spoonful of the tuna salad mixture.
06 - Finish with diced cucumber, sliced radishes, chopped pickled ginger, additional sesame seeds, and microgreens or cilantro. Serve immediately while the rice remains crispy.