Wet your hands a bit, then take about 2 tablespoons of rice and shape it into a 2 1/2-inch (6 cm) oblong ball. Repeat with the remaining rice, you should get about 8 pieces.
Take the salmon out of the fridge. Using a very sharp knife (holding it at a 30° angle), finely slice the salmon against the grain.
Spread a small amount of wasabi onto each rice ball, and cover with a salmon slice.
Serve with soy sauce and pickled ginger, if desired.