Lay sushi roller mat on table. Cover with Nori sheet. Using wet hands or back of a wet spoon, evenly cover Nori sheet with thin layer of rice. Cover rice with plastic wrap. Flip such that the Nori sheet is facing upwards. Place small pieces of salmon and scallions near bottom edge of Nori sheet. Roll Nori sheet from front to back, using sushi mat as guide. Be careful not to include the seran wrap in the roll. Cut roll into slices, using sharp knife. Mix wasabi powder with small amount of water until the correct consistency. Serve rolls with wasabi, ginger and soy sauce.
1 Nori sheet makes about 6 to 7 small rolls.