Rinse the rice under cold water until the water runs clear. Combine with boiling water in a saucepan, cover, and cook over low heat until tender and the water is absorbed, 15 to 20 minutes. Remove from heat and rest, covered, 10 minutes.
Heat the rice vinegar, salt, and sugar until dissolved. Transfer the rice to a bowl, pour the seasoning over, and fold gently with a spatula. Let cool to room temperature.
Lightly oil a donut pan. Arrange radishes, avocado, cucumber, salmon, and nori snugly in each cavity. Pack in rice and press firmly with a damp spoon to compact. Invert and release carefully.
Drizzle with spicy mayonnaise and teriyaki. Finish with caviar and sesame seeds. Serve immediately.