Make the Rice: Rinse the rice until the water runs clear. Cook in a rice cooker or according to package directions. Combine the rice vinegar, sugar, and salt in a small bowl, then fold it into the cooked rice with the sesame seeds. Cover and refrigerate for at least 3 hours, overnight is preferred.

Spicy Scallop Mixture: Pat the scallops dry with paper towels. Combine in a bowl with the Japanese mayo, sriracha, sesame oil, rice vinegar, tamari, and scallions. Mix until evenly coated.

Citrus Tamari Sauce: Combine the cilantro, chopped serrano, orange juice, and lemon juice in a small bowl. Stir in tamari to taste.

Assemble the Cake: Preheat the broiler. Coat the springform pan with cooking oil spray. Press half of the seasoned rice into the bottom of the pan. Layer in the crushed nori, avocado slices, and cucumber slices. Press the remaining rice firmly on top and add another light layer of crushed nori. Top with the scallop mixture in an even layer.

Broil: Broil for 2 to 4 minutes, watching closely. The scallops should caramelize on top without warming the layers below. Remove the springform sides.

Top and Serve: Squeeze about 1 tbsp Japanese mayo in an S pattern over the top, then the same with sriracha. Sprinkle with shichimi togarashi and place the serrano slices around. Serve with the citrus tamari sauce on the side.