In a small glass bowl, combine the cooked sushi rice with rice vinegar and sea salt until the rice is evenly seasoned.
Slice the sashimi-grade tuna and the cucumber into long, thin matchsticks about 4 inches in length.
Slice the avocado into thin wedges and set aside on a clean cutting board.
Place one nori sheet on a bamboo sushi rolling mat with the shiny side facing down.
Wet your fingers slightly and spread half of the seasoned rice evenly over the nori, leaving a 1-inch border at the top edge.
Arrange half of the tuna strips, cucumber matchsticks, and avocado wedges in a horizontal line across the center of the rice.
Using the bamboo mat, roll the nori tightly from the bottom up, applying gentle pressure to ensure a firm roll.
Lightly moisten the top border of the nori with water to seal the roll completely.
Repeat the process with the second nori sheet and the remaining ingredients.
Using a very sharp, slightly damp knife, slice each roll into 8 uniform pieces and sprinkle with toasted sesame seeds.
Serve the rolls immediately with coconut aminos and wasabi paste for a clean, zesty finish.