In a medium bowl, combine the drained skipjack tuna, Greek yogurt, lime juice, lime zest, sriracha, sea salt, and black pepper.
Mix the ingredients thoroughly until the tuna is well-flaked and evenly coated in the creamy dressing.
Place one nori sheet on a bamboo rolling mat or a clean, dry flat surface.
Spread 0.25 cup of the cooked sushi rice in a thin, even layer over the bottom two-thirds of the nori sheet.
Arrange half of the tuna mixture in a horizontal line across the center of the rice layer.
Layer half of the avocado slices and half of the julienned cucumber directly on top of the tuna.
Lightly moisten the top edge of the nori sheet with a small amount of water using your fingertip.
Carefully roll the nori from the bottom edge upward, keeping the filling tight and pressing firmly to seal at the damp edge.
Repeat the assembly process with the second nori sheet and the remaining ingredients.
Use a sharp, wet knife to slice each roll into 6-8 uniform pieces and serve immediately with coconut aminos for dipping.