Step 1: Prepare the Sushi Rice

1. Rinse the sushi rice under cold water until the water runs clear to remove excess starch.
2. Combine the rice and water in a saucepan, cover, and bring to a boil. Reduce the heat to low and simmer for 15 minutes.
3. Remove from heat and let the rice sit, covered, for 10 minutes.
4. In a small bowl, mix the rice vinegar, sugar, and salt until dissolved. Gently fold this mixture into the cooked rice. Let the rice cool to room temperature.

Step 2: Make the Nori Taco Shells

1. Preheat the oven to 300°F (150°C).
2. In a small bowl, whisk together the flour, water, and sesame oil to create a light batter.
3. Brush one side of each nori sheet with the batter. Fold the nori sheets in half, pressing lightly to adhere.
4. Drape the nori sheets over the rungs of an oven rack to create a taco shape. Bake for 10 minutes or until crisp. Remove and let cool.

Step 3: Prepare the Fillings

1. Dice the sushi-grade fish and toss it with soy sauce, sesame oil, and sriracha for added spice if desired.
2. Prepare the vegetables: julienne the cucumber and carrot, and slice the avocado.

Step 4: Assemble the Sushi Tacos

1. Spread a layer of sushi rice inside each nori shell.
2. Add a portion of the marinated fish, followed by the sliced avocado and julienned vegetables.
3. Top with sesame seeds, scallions, pickled ginger, and a drizzle of wasabi mayo or spicy mayo.

Step 5: Serve and Enjoy

1. Serve the tacos immediately to enjoy their crisp texture. Pair with soy sauce and additional pickled ginger on the side.