Whisk together all tempura batter ingredients until slightly lumpy.
Dip nori sheets into the tempura batter, ensuring they are well-coated.
Fry the nori in batches until golden brown and crispy (about 1-2 minutes). Drain excess oil on a paper towel-lined plate.
While still warm, shape fried nori sheets into taco shells by draping them over the edges of an inverted muffin tin or shaping them by hand. Allow to cool completely.
For the taco filling:
Cook squid as per packet instructions.
Line the bottom of the taco shells with rice, cucumber, top with squid then drizzle with yum yum sauce and sriracha if using. Serve immediately.