Break the cauliflower into florets and place them in a blender. Blend it until it looks like fine rice.
Place a large nonstick frying pan over medium-high heat. Add the riced cauliflower and cook, stirring frequently, until it's fork-tender, about 7-10 minutes.
Place the warm cauliflower in a bowl along with the vinegar and mix well. Place the mixture in the fridge to cool completely, which takes around 30 minutes.
While the rice is cooling, slice the salmon, avocado, and cucumber, which will be your fillings. Set aside.
Once the cauliflower rice has cooled, begin assembling your sushi rolls. Place a nori sheet shiny side down on a sushi mat. Top with some of the cooled cauliflower rice mix.
Spread the rice evenly on the sheet, leaving a 1- to 2-inch gap at one end.
Add your filling ingredients. Roll firmly until you reach the edge of the rice. Sprinkle some water on the exposed end of the nori sheet, finish rolling, and seal the edge of the sheet with your finger. Use the sushi mat to firm up the roll.
Remove the mat and cut the roll into 8 slices. Repeat the process with the other nori sheets and the rest of your cauliflower rice and fillings.
Garnish with toasted sesame seeds, if desired. Serve immediately with soy sauce or Worcestershire sauce.