Season the cooked sushi rice with rice vinegar and sea salt, stirring gently to combine.
Slice the sushi-grade tuna into long, thin strips approximately half an inch thick.
Julienne the cucumber into matchsticks and slice the avocado into thin wedges.
Place a nori sheet on a bamboo rolling mat and spread half of the rice evenly over the surface, leaving an inch at the top edge.
Layer half of the tuna strips, cucumber matchsticks, and avocado wedges across the center of the rice.
Roll the nori tightly using the mat, wetting the top edge with a little water to seal the roll.
Repeat the process with the second nori sheet and the remaining ingredients.
In a small bowl, whisk together the coconut aminos, toasted sesame oil, grated fresh ginger, and sriracha.
Slice the sushi rolls into bite-sized pieces using a sharp, wet knife and garnish with thinly sliced scallions before serving with the dipping sauce.