Cook rice in 4 cups of spring water for 45 minutes, let it cool down.
Cut the sheet of nori in half.
Put 1 piece each of carrot, cucumber and avocado in it and roll the nori around it using a sushi mat.
Continue to roll the nori sheet until all the vegetables are finished.
When the rice is cool, wet the sushi mat in water and put it on a cutting board.
With wet hands, put rice in the sushi mat in a thin layer, but only cover one half of the mat.
Then, with the fingers spread a small portion of umeboshi plum paste in the center of the rice, along the part where the nori roll will be placed.
Roll the sushi mat in a way so the rice covers the entire nori.
Press with the hands the rolled up sushi mat and fix the end pieces.
Unroll the mat. You will have a little tube of rice.
Roll it in a plate covered with the sesame seeds.
Cut into 1″ pieces using a very sharp knife.