1. Rinse the rice well with cold water then boil the rice; follow the directions on the package.
2. When the rice is done boiling, mix in 2 tbsp. rice vinegar and leave to cool.
3. Cut the salmon into thin slices, and the cucumber into thin strips.
4. When the rice is cooled down: put a seaweed sheet on top of the sushi mat with the shiny side facing down.
(It works best if you wet your hands a little when you spread the rice out on the seaweed sheet, so that the rice isn't too sticky.)
5. Spread out ¼ of the rice evenly onto the seaweed sheet, but be sure to leave about 1.5 cm. free of the edge farthest away from you (this is for later use when we are going to "glue" the sushi roll shut.)
6. Then put the salmon pieces on top of the rice in the middle, and put some cucumber strips in a line on top of the salmon, so that it covers the whole width of the seaweed sheet.
7. Roll the seaweed sheet with the filling together as tightly as possible, with the help of the sushi mat. Wet the empty space of the seaweed sheet before closing all the way, so that it sticks better together.
8. Proceed by making the other 3 rolls in the same way, and then let the sushi rolls rest in the refrigerator for 10 min.
9. Cut the rolls into proper size pieces, about 8 per roll.
10. Serve with soy sauce, wasabi and pickled ginger.