To make the sushi rice

1. Place the rice and water into a rice cooker and cook according to the manufacturer instructions. Once done, season with the rice vinegar, sugar and salt and set aside to cool.

To make the tempura batter + mushrooms

1. Combine the AP flour, cornstarch and baking powder into a large bowl. Add in the ice-cold fizzy water and stir until smooth.
2. Place several inches of oil into a small, cast iron pot (I like this one). Bring it to 350 degrees over medium-high heat. The oil will be ready to use in 5-7 minutes. You can tell when it’s ready by inserting a dry chopstick into the hot oil so it touches the bottom of the pot. If bubbles form around it immediately, you are ready to fry.
3. Toss all of the mushroom pieces into the tempura batter. It will be a little goopy. Move the pieces around until they are coated all over. Drop several pieces into the hot oil, one by one, taking care not to overcrowd the pot. Allow to fry for a couple of minutes, flip with chopsticks or a skimmer and fry for a minute or two more. Place onto paper towels to drain and repeat the process with the rest of the mushrooms.

To assemble the rolls

1. Divide the cooled rice into 4 portions. Slide a sushi mat into a large Ziploc bag or cover with plastic wrap. Place one sheet of nori, shiny side down, on the mat. Moisten your fingers with some water to prevent rice from sticking to them, then spread the rice evenly over the nori sheet, leaving about an inch exposed at the top. Sprinkle with a teaspoon of sesame seeds.
2. With the exposed end away from you, place 4 or 5 pieces of the tempura mushrooms in a line along the side closest to you. Add a couple slices of avocado and about a tablespoon of the kimchi mayo.
3. Roll the sushi away from you, gripping the mat tightly but gently. Once rolled, seal the end with water or add a few grains of rice to the end to help seal.
4. Cut the sushi in half with a very sharp knife (I run the blade under scalding water for a cleaner cut), then each half into halves, then those halves into halves to make 8 pieces.
5. Place onto a serving plate, repeating the process to make 4 rolls. Top with some of the sliced scallions.
6. Serve immediately with the soy sauce and pickled ginger and wasabi.