Mix the ranch poweder into the japanese mayo a little a time until you're happy with the flavor. I typically prepare this in a ½ cup batch which I store in the fridge for future use, but to prepare for just one roll mix a few tablespoons of mayo with a teaspoon of the powder then adjust to taste.
Cover the sheet of nori in a thin even layer of rice, filling all the way out to the edges. (click for guide)
Flip the sheet of nori over so the rice is face down on a bamboo rolling mat that is wrapped in plastic. (click for guide)
Arrange the fillings (shrimp tempura and avocado) in even lines, 1 inch from the edge along the longer side of the nori sheet. (click for guide)
Spoon the spicy tuna over the top of the roll as evenly as possibe. (click for guide)
Place the plastic-wrapped rolling mat over the top of the roll and press the roll into a consistent shape. Be gentle with this step so you don't squeeze out the spicy tuna. (click for guide)
Place the roll on a cutting board and grab your sharpest knife. Optionally, cover the roll with plastic cling wrap. Run the knife under water for a second, then shake off any excess. Cut the roll into 8 equal pieces using a gentile sawing motion with the knife, running the knife under the water between every 2-3 cuts to prevent sticking. (click for guide)
Plate the roll on your serving dish. Drizzle with the ranch mayo the top with crispy onions. (click for guide)
Notes
If this is your first time making sushi be sure to check out the Sushi Beginner's Guide before getting started!