Place the rice in a pan and cover with water. Bring to the boil and cook on a high heat for 15 minutes. Turn the heat to low and simmer the rice for a further 3-4 minutes, making sure all the water has been absorbed and the rice is tender.
Meanwhile, place the salmon, mayonnaise, mirin, sriracha and coriander stems in a bowl and mix.
Spread the warm rice out on a baking tray. Mix the seasoned rice vinegar and sugar together until the sugar dissolves, then sprinkle over the rice.
Measure 2 tablespoons of rice and form into a rough ball. Press a hole into the center of the rice ball and stuff with a tablespoon of the salmon mixture. Seal in the salmon mixture and roll the ball between your hands to form a small ball. Repeat the process until all the rice and salmon are used.
Beat the egg in a small bowl. Place the breadcrumbs and sesame seeds in a shallow dish. Coat the rice balls with the egg and then roll in the breadcrumbs.
Heat the oil in a deep-fat fryer or in a deep, heavy-based saucepan to 190C. (CAUTION: Hot oil can be dangerous; do not leave unattended). Deep fry the rice balls for 2-3 minutes, or until golden-brown.
Meanwhile, for the oyster sauce mayonnaise, combine the mayonnaise, oyster sauce, and sriracha paste in a small bowl.
Serve the rice balls hot with the oyster sauce mayonnaise and garnish with coriander and amaranth.