Cure the salmon: Mix the salt and sugar in a bowl. Place 2 long pieces of plastic wrap on a work surface, overlapping them to form a cross. Put half of the cilantro sprigs in the middle of the plastic wrap and top with half of the salt-sugar mixture. Press the salmon into the mixture, making sure the bottom of the fish is covered with salt and sugar. Sprinkle the salmon with the remaining salt-sugar mixture and rub it in, then place the rest of the cilantro on top. Wrap tightly in the plastic and refrigerate for 24 hours.
The next day, unwrap the salmon, rinse off the salt and pat dry. Cut into 1/4-to-1/2-inch cubes.
Make the salad: Toss the salmon, cilantro, tomatoes, scallions, jalapeno, vegetable and sesame oils and lime juice in a bowl. (Traditionally, the cured salmon is flaked and "massaged" with the other ingredients by hand.) Garnish the salad with chopped macadamia nuts, if desired.