Rinse and strain the rice, leave it in the colander for about 30 minutes, then cook in a rice cooker. While the rice is cooking, squeeze the grapefruit using a juicer.
Transfer the cooked rice to a bowl and add the grapefruit juice, lemon juice and salt. Make sushi rice by mixing it quickly with a moistened rice scoop.
Boil the canola flowers, then chop half finely for sushi rice, and cut the other half into 4 cm strips for garnish. Shell and boil the broad beans, remove the skins, then chop coarsely for sushi rice, leaving a few whole beans to use as a garnish.
Divide the sushi rice into three equal portions. Leave one portion plain, mix one with chopped canola flowers, and mix the last one with chopped broad beans.
Topping: Slice the salmon, tuna and scallops. Boil the prawns in salted water and cut them in half.
Topping: Crack the egg into a bowl, beat it, and mix in a pinch of salt and sugar. Heat up the lightly oiled frying pan, pour in the mixture and make a thin, flat omelet. Cut the omelet into thin strips.
Topping: Fold the shiso leaves in half lengthwise. Slice avocado, mango, kiwifruit and cheese into small pieces.
Place a topping on cling wrap, then place a small dollop of the sushi rice you prepared in Step 4. Gather the edges of the cling wrap together, twist and squeeze it to make a neat ball. Remove the cling wrap. Repeat until all the sushi rice is used up. Place the sushi balls on a serving dish and use the garnish ingredients to decorate them.