Place the warm cooked sushi rice in a bowl and gently fold in the rice vinegar and sea salt until combined.
Slice the sashimi-grade tuna and the avocado into long, thin strips.
Julienne the cucumber into thin matchsticks.
Lay the nori sheet on a bamboo sushi rolling mat and spread the seasoned rice evenly over the surface, leaving a one-inch border at the top.
Arrange the tuna strips, avocado, and cucumber matchsticks in a horizontal line across the center of the rice.
Using the bamboo mat, roll the nori tightly over the filling, applying gentle pressure to create a firm cylinder.
Use a very sharp, wet knife to slice the roll into 8 even pieces.
In a small ramekin, whisk together the sesame oil, sriracha, and coconut aminos.
Drizzle the sauce over the rolls and garnish with sesame seeds before serving.