In a small bowl, fold the rice vinegar into the warm cooked sushi rice and let it cool to room temperature.
Slice the sushi-grade salmon into thin strips and julienne the cucumber and avocado into long, slender pieces.
Place one nori sheet on a bamboo rolling mat, then spread half of the seasoned rice evenly over the bottom two-thirds of the sheet.
Arrange half of the salmon, shrimp, cucumber, and avocado in a horizontal line across the center of the rice.
Lift the edge of the mat 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 remaining ingredients, then use a sharp, wet knife to slice each roll into six even pieces.
Serve the fresh rolls immediately with wasabi paste, pickled ginger, and tamari for dipping.