1. Rough chop the cauliflower into small pieces (about ¼ inch or a bit over ½ cm cubes). Heat a wok over medium low heat, pour in 1 tablespoon of oil to coat the bottom and toss in half of the cauliflower rice. Cover with a lid to keep in the moisture. Lift lid and toss every few minutes. Cook to al dente stage. Transfer to a bowl and repeat with the second batch. Set aside to cool to room temperature
3. To the small bowl also add the water and the chia seeds. Stir well. Let rest until the chia seeds have swelled or bloomed, about 15 – 20 minutes. Distribute the chia seeds over the seasoned cauli-rice, fold to combine and distribute throughout the mixture. Set aside
5. To assemble the sushi roll: lay a sheet of nori, shiny side up, onto a sushi mat. Scoop 1 cup of prepared sushi cauli rice and distribute evenly over the bottom 2/3 of the nori sheet. Using a 1 tbsp measure, scoop and place 4 tbsp of the spicy tuna along the bottom and over the cauli rice. Distribute a quarter of the Vietnamese daikon and carrot pickle along the side of the tuna.
6. Take hold of both the nori and the sushi mat, and roll the mat over the filling as you squeezing down gently. Lift the mat and roll and squeeze until the cauli rice has been rolled. Wet the nori edge along its length and finish rolling to make a nice tight roll. Squeeze down all along the length to help the roll hold its shape.
7. Transfer the roll onto a cutting board. Wipe the blade of a serrated knife with a damp towel before and in between slices. To get 8 even cuts, first cut the roll in half, then each half in half and then each quarter in half, this will result in 8 equal sections