Wash the rice and place in a pan with the water. Bring to the boil, reduce the heat to simmer, cover and cook for 35 minutes.
While the rice is cooking, grind the sesame seeds and sea salt to a coarse powder.
When the rice is cooked, transfer it to a wide flat dish, cover with a tea towel and leave to sit for 10 - 15 minutes.
Mix the rice vinegar and maple syrup together. Pour the vinegar and syrup mix through the rice and using a wooden spoon cut through the rice to break up any lumps and ensure the vinegar is covering all the rice grains. Fan the rice for 5 minutes so it cools quickly.
Slice the avocado and drizzle the umeboshi over the slices. Score the skin of the cucumber and cut it into thin lengths.
Lay a couple of nori sheets out on a board at one time. Brush each sheet with water so it's slightly damp and malleable (but not soaking). Lay a large spoonful of rice about 6 cm across the front of each sheet of nori and sprinkle the sesame salt over the rice. Top with a length of cucumber and avocado and roll it up to a long sausage shape.
Continue until the rice is used up.
Cut the nori into pieces with sharp knife.
Tip: When cutting nori, wet the blade of the knife with cold water.