In a small bowl, combine the warm cooked sushi rice with rice vinegar and sea salt until the grains are lightly coated and sticky.
Slice the sushi-grade salmon into long, uniform strips approximately half an inch in thickness.
Cut the avocado and cucumber into thin, even matchsticks to ensure a balanced roll.
Lay the nori sheet on a bamboo rolling mat and spread the seasoned rice in a thin layer over the bottom two-thirds of the sheet.
Place the salmon strips, avocado, and cucumber in a horizontal line across the center of the rice layer.
Lift the edge of the mat and roll the nori tightly over the filling, applying gentle, even pressure to create a firm cylinder.
Using a very sharp, slightly damp knife, slice the roll into eight equal pieces to prevent tearing the nori.
Garnish the rolls with sesame seeds and serve immediately with a side of tamari for dipping.