Heat the vinegar and sugar in a small saucepan over medium heat until the sugar is dissolved. Prepare brown rice according to package instructions.
While your brown rice is still warm, pour the vinegar-sugar mixture and soy sauce over it and toss to combine. Let cool to room temperature. Adding the soy sauce to the rice saves you from having to lug soy sauce to school or work.
Use a sharp knife or kitchen shears to cut up your nori.
Shred carrot and cut cucumber into matchsticks. When preparing the vegetables, place the diced avocado in a bowl and toss with just enough lime juice to lightly coat in order to prevent browning.
Once ingredients are ready, simply add one layer at a time and use a spoon to level and pat down each layer. If you smudge the sides of the jar, wipe the inside with a dry cloth. I used half the sheet of nori on the bottom and half on top, and finished with ginger and wasabi to taste.