Lay one nori sheet on a clean, dry surface. Cut the 2nd nori sheet in half and place them as it's shown in the pic.
Spread the cooked sushi rice evenly on the bottom 1/4 part of the nori sheet, leaving a small border at the bottom.
Place the sliced salmon or your preferred sushi-grade fish on top of the rice, covering the next 1/4 part of the nori sheet.
Layer the thinly sliced avocado on the third part of the nori sheet, right above the fish.
Add the sliced cucumber, covering the final 1/4 part of the nori sheet.
Starting from the bottom (rice-covered part), carefully wrap the nori sheet as it's shown. Once the nori is fully wraped, use a little water on the border to seal the sushi sandwich.
Use a sharp knife to cut the sushi sandwich into half. Serve your simple sushi sandwich with soy sauce and wasabi on the side for dipping. Enjoy!