Steam the cauliflower rice until tender, then spread it on a tray to cool slightly.
Mix the rice vinegar and sea salt into the cauliflower rice until well combined.
Slice the sushi-grade salmon into long, thin strips and halve the cooked shrimp lengthwise.
Prepare the cucumber and carrot into thin matchsticks and thinly slice the avocado.
Place one nori sheet on a bamboo rolling mat and spread half the cauliflower rice evenly over the bottom two-thirds.
Arrange half of the salmon, shrimp, cucumber, carrot, and avocado in a horizontal line across the center of the rice.
Roll the nori tightly from the bottom, using the mat to maintain a firm shape, and seal the edge with a drop of water.
Repeat with the second sheet and remaining ingredients, then slice each roll into eight pieces using a sharp, wet knife.
Sprinkle with sesame seeds before serving.