Sauté the cauliflower rice in a dry pan over medium heat for 5 minutes until tender, then let it cool completely in a bowl.
Stir the rice vinegar and sea salt into the cooled cauliflower rice until well combined.
Slice the ahi tuna, cucumber, and red bell pepper into thin matchsticks, and shred the carrot.
Place one nori sheet on a bamboo rolling mat and spread half of the cauliflower rice evenly over the bottom two-thirds of the sheet.
Layer half of the tuna, shrimp, avocado, cucumber, carrot, and bell pepper across the center of the rice.
Roll the nori tightly from the bottom up, using the mat to guide it, and seal the edge with a drop of water.
Repeat with the second nori sheet and remaining ingredients.
In a small bowl, whisk together the tamari, grated ginger, lime juice, and black pepper.
Slice each roll into 8 pieces using a sharp, wet knife and serve immediately with the dipping sauce.