For Ginger Wasabi Mayo, combine all ingredient in bowl. Cover and refrigerate.
For Spicy Tuna, combine all ingredients in bowl. Cover and refrigerate.
For Rice Cakes, season cooked rice with rice vinegar and sugar. Line a small cookie sheet with waxed paper and spread rice into 1/2-inch thick layer. Cut out rounds with a 3-inch cutter. (Rice can be remolded if you didn't quite get 6) Place rice rounds on a waxed paper-lined cookie sheet. Sprinkle with black and white sesame seeds and freeze at least 1 hour.
Preheat oil in a deep Dutch oven to 350°. Carefully fry rice cakes until golden brown.
Shingle cucumber slices over each rice cake and top with shiso leaves and sliced avocado. Top with a hefty scoop of Spicy Tuna, a dollop of Ginger Wasabi Mayo, a squeeze of Sriracha, a sprinkling of sesame seeds and one thinly sliced round of Serrano. Serve with soy sauce for dipping.