In a food processor, add your chopped cauliflower florets and pulse until it reaches the consistency of rice.
Transfer the rice into a microwave safe bowl and sprinkle with salt. Microwave for 4-5 minutes, until soft and tender. Remove excess moisture and let it cool completely. Once cool, add the vinegar and powdered sugar and mix until combined.
Place your nori sheets on a flat surface. Divide the cauliflower sushi rice amongst the two sheets, reserving 1/4 of an inch around the perimeter of it.
Spread the mayonnaise on each roll, followed by the salmon and cucumber, then sprinkle with sesame seeds. If using wasabi, spread a thin layer down the side.
Roll up each roll very tightly, removing any of the filling that seeps out. Using a sharp and slightly wet knife, slice the sushi into pieces.
Notes
TO STORE: Leftover sushi can be stored in the refrigerator, covered, for up to 3 days. TO FREEZE: Place sushi in a shallow container and store it in the freezer and it will keep well for up to 2 months. You must let it thaw completely before serving.