How to Make It
In a medium saucepan, combine the rice with 1 3/4 cups of the water and 1 teaspoon of salt and bring to a boil over moderately high heat. Cover, reduce the heat to very low and cook without stirring until all of the water is absorbed and the rice is tender, about 25 minutes. Fluff the rice with a fork and stir in the coconut milk. Transfer the rice to a baking sheet and spread it out to a 9-inch square, about 1/2 inch thick. Press a piece of plastic wrap directly on the rice and refrigerate until chilled.
In a small bowl, combine the wasabi powder with the remaining 1 tablespoon of water and mix to a paste. Using a 1 1/2 -inch round cookie cutter, cut the rice into individual cakes. Spread a scant 1/8 teaspoon of the wasabi paste on each rice cake and arrange a strip of smoked salmon on top. Garnish with the arugula and serve at room temperature.