Prepare the sushi rice by tossing it with rice vinegar and sea salt while still warm, then let it cool completely to room temperature.
Slice the sushi-grade salmon into long, thin strips approximately half an inch thick using a very sharp knife.
Peel the avocado and slice into thin wedges, and julienne the cucumber into delicate matchstick-sized pieces.
Place a sheet of nori on a bamboo rolling mat, shiny side down, with the lines running horizontally.
Spread a very thin layer of the seasoned rice over the bottom two-thirds of the nori, leaving the top edge clear for sealing.
Arrange the salmon strips, avocado wedges, and cucumber matchsticks in a horizontal line across the center of the rice-covered area.
Carefully roll the nori from the bottom, using the bamboo mat to apply gentle, even pressure until a tight cylinder is formed.
Moisten the top edge of the nori with a small amount of water to seal the roll securely.
Slice the roll into 8 even pieces and serve immediately with coconut aminos, wasabi, and pickled ginger.