Make the Low-Carb ‘Rice’: Grate or pulse the cauliflower florets in a food processor until it resembles rice grains (about 3 cups). Heat a large skillet over medium heat and add the cauliflower rice. Stir occasionally for 5-7 minutes until tender and any moisture evaporates. Stir in rice vinegar, sesame oil, and a pinch of salt. Let it cool to room temperature.

1. Assemble the Sushi Rolls: Place a sushi rolling mat or bamboo mat on a clean surface, with a sheet of nori shiny-side down. Spread the cooled cauliflower rice evenly over the nori sheet, leaving 1/2 inch at the top. Add the fish, avocado, cucumber, and carrots (if using) in a neat line across the center of the rice.
2. Roll the Sushi: Start rolling from the bottom using the mat to keep the roll tight. Seal the top edge of the nori by dampening it with water.
3. Slice the Roll: Using a sharp knife, slice the roll into bite-sized pieces, cleaning the knife between cuts for clean slices.
4. Serve: Arrange the rolls on a platter, sprinkle with sesame seeds, and serve with soy sauce, pickled ginger, and wasabi if desired.