Pat the shrimp dry then season on both sides with salt and white pepper
Heat a medium skillet over medium heat then add the avocado oil
Sear the shrimp for 2-3 minutes on each side or until completely opaque and cooked through then set aside to cool
Roughly chop the shrimp (remove the tails if they are still on) then add to a medium bowl
Combine the shrimp with the soy sauce, Kewpie mayonnaise and Sriracha chili sauce
Heat the oil in a large sauté pan with high sides until shimmering and about 325℉/170℃ (or test it by inserting the end of a chopstick; if it bubbles, it's ready)
While the oil is heating, make the tempura batter; in a medium bowl, whisk together the flour and cornmeal
Create a well in the dry ingredients or move them to one side of the bowl and add the egg; gently beat the egg
Slowly pour in the water while mixing until the flour and cornstarch are incorporated and a thin batter forms; mix gently and do not overmix the batter (see Note 6)
One at a time, dip one side of the nori sheet into the batter and allow excess batter to drip off (see Note 6) then carefully place, battered side down, into the oil
Fry for 30 seconds then carefully flip using tongs and fry for an additional 15 seconds until crispy (the batter will not really darken and will be very lightly golden)
Repeat with the additional seaweed sheets, setting aside fried seaweed shells on a paper towel lined plate, battered side up
Assemble the tacos by adding about 2 tbsp of cooked rice to each shell, then about 2 tbsp of the spicy shrimp, then the cucumber, avocado, green onions, sesame seeds (or any other toppings you want); drizzle with Kewpie mayonnaise and Sriracha to taste, fold and serve