Season the warm cooked sushi rice with rice vinegar and sea salt, then let it cool completely to room temperature.
Slice the sushi-grade ahi tuna and the cooked, peeled shrimp into long, thin strips suitable for rolling.
Julienne the cucumber into matchsticks and thinly slice the avocado.
Place one nori sheet on a bamboo rolling mat and spread half of the seasoned rice evenly over the bottom two-thirds of the sheet.
Layer half of the tuna, shrimp, avocado, and cucumber matchsticks across the center of the rice.
Carefully roll the nori from the bottom up, using the mat to apply gentle, even pressure to create a tight, uniform cylinder.
Repeat the process with the second nori sheet and the remaining ingredients.
Use a very sharp, wet knife to slice each roll into 6 to 8 even pieces, wiping the blade between cuts.
Garnish the rolls with sesame seeds and serve immediately with coconut aminos for dipping.