In a small bowl, gently fold the rice vinegar and sea salt into the warm cooked sushi rice until well combined and slightly sticky.
Slice the salmon, ahi tuna, avocado, and cucumber into long, thin uniform strips.
Place one nori sheet on a bamboo sushi rolling mat with the rough side facing up.
Spread half of the seasoned rice evenly over the nori, leaving about an inch of space at the top edge.
Arrange half of the salmon, tuna, avocado, cucumber, and carrots in a horizontal line across the center of the rice.
Using the mat, roll the nori tightly over the fillings, applying gentle pressure to create a firm cylinder.
Wet the top edge of the nori with a little water to seal the roll completely.
Repeat the process for the second roll with the remaining ingredients.
Using a very sharp, damp knife, slice each roll into 6 to 8 pieces.
Serve the rainbow rolls immediately with wasabi paste and tamari for dipping.