Makes 6 rolls
Rinse and drain rice three times or until the rinse water is clear. Add water, soak for 45 minutes, and bring to a boil. Cover, cook for 45 minutes over low heat, and let rice sit for 10 minutes before removing lid.
Stir in brown rice vinegar. Squeeze juice from ginger and add to rice. While rice cools, boil water in a small pot. Drop carrot matchsticks into the boiling water for 1 minute. Remove carrots and rinse under cold water to stop cooking. Drop green onions into boiling water for 30 seconds, remove, and rinse under cold water.
Lay 1 sheet of nori, shiny side down, on a bamboo sushi mat. Lightly spread umeboshi paste or mustard over the nori. Wet hands and spread cooked rice about 3/8 inch thick over nori, covering all but a one inch strip at both the top and bottom. Place strips of carrot and green onion horizontally in the middle of the rice. Sprinkle with sesame seeds.