Wash the rice a few times in cold water and drain. Cook following the directions on the packet but as a general rule you will need 1 1/8 cups of water to 1 cup of rice. Simmer for about 20 minutes then take off the heat and let stand for another 15-20 minutes. Do not remove the lid, no peeking allowed.
Transfer the rice to a glass bowl to cool completely and add the mirin or rice vinegar, if using. Very carefully stir through you don’t want to break down the rice.
While the rice is cooking and cooling prepare the other ingredients. Grate the carrot and transfer to a bowl. Mash the avocado with a little lemon juice to stop it discolouring. Top and tail the green beans and cook in boiling water for two minutes, no longer. You just want to blanche the beans they still need a crunch. Remove the beans from the heat and rinse with cold water to stop the cooking process.
Once the rice has completely cooled you’re ready to make the maki sushi. On a folded T-towel (or sushi mat if you have one) place a sheet of nori seaweed and top with rice. Top with a line of grated carrot, a line of mashed avocado and then top with a line of beans.
Take the edge of the T-towel/sushi mat and carefully start to roll the sheet of nori, don’t worry you may lose some rice. Brush a little water on the far edge of the nori seaweed so it sticks together and forms a roll.
Wrap the roll in cling film and put in the fridge for 30 minutes. Unwrap and carefully slice into rounds, the end rounds will be messy but that’s the chef’s treat. Serve with a small bowl of soy sauce to dip into and a dot of wasabi, careful its hot!