2.Cook rice in large saucepan of boiling water until tender; drain. Spread warm rice in lightly oiled 40cm x 25cm (16-inch x 10-inch) baking tray; smooth surface with damp hands. Sprinkle with seeds; press down to adhere. Cool to room temperature.
3.Cut rounds from rice using 9cm (3¾-inch) cutter; place on oven tray lined with baking (parchment) paper. Spray with cooking oil; bake 15 minutes. Turn; bake another 15 minutes or until slightly crisp. Keep warm.
4.Meanwhile, heat oil in large frying pan; cook chicken, skin-side down, until golden. Turn; cook until browned and cooked through. Remove from pan.
5.Bring sauce, mirin, sake and sugar to the boil in same pan. Reduce heat; simmer until sauce thickens. Return chicken to pan; turn to coat.
6.Sandwich chicken, cucumber, rocket and mayonnaise between rice rounds.
Any leftover rice is perfect for making fried rice.