Pulse cauliflower in a food processor until it reaches a rice-like consistency, then lightly sauté in a pan with rice vinegar and sea salt until tender.
Slice the sashimi-grade ahi tuna, cucumber, and avocado into uniform, thin matchsticks for easy rolling.
In a small ramekin, whisk together the avocado oil mayonnaise and sriracha to create a clean, spicy aioli.
Place a nori sheet on a bamboo sushi mat and spread a thin, even layer of the prepared cauliflower rice over the bottom two-thirds of the sheet.
Arrange the tuna strips, cucumber, avocado, and freshly grated ginger horizontally across the center of the cauliflower rice.
Roll the nori tightly away from you using the mat to guide it, sealing the final edge with a small amount of water.
Slice the roll into eight even rounds using a sharp, wet knife and serve immediately with coconut aminos and a sprinkle of black sesame seeds.