In a small bowl, gently fold the rice vinegar and sea salt into the warm cooked sushi rice and let it cool to room temperature.
Slice the sushi-grade salmon into long, thin strips approximately half an inch thick.
Peel and slice the avocado and cucumber into thin matchsticks.
Place one sheet of nori on a bamboo rolling mat, shiny side down.
Using wet fingers, spread half of the seasoned rice in a very thin, translucent layer over the bottom two-thirds of the nori sheet.
Arrange half of the salmon strips, avocado, and cucumber in a horizontal line across the center of the rice.
Lift the edge of the bamboo mat closest to you and roll the nori tightly over the fillings, applying gentle pressure to create a firm cylinder.
Repeat the process with the second nori sheet and the remaining ingredients.
Use a very sharp, slightly damp knife to slice each roll into 6 to 8 even pieces.
Serve immediately with coconut aminos, wasabi paste, and pickled ginger on the side.