1. Cook the sushi rice according to the instructions on the packaging. Once cooked, let it cool.
2. In a bowl, mix the rice vinegar, sugar, and salt. Set aside.
3. Cut the avocado, cucumber, and carrots into thin slices. Set aside.
4. Place the spinach sprouts in a hot pan and lightly sauté them. Set aside.
5. Moisten your hands to prevent the rice from sticking. Take a small portion of rice and flatten it in the palm of your hand.
6. Place a slice of avocado, cucumber, carrot, and spinach sprouts in the center of the rice.
7. Close it all up by forming a ball and pressing lightly to ensure the ingredients are well held together.
8. Cut a sheet of nori into thin strips and wrap them around the onigiris to decorate them.