Bloom the gelatin: In a small bowl, sprinkle the gelatin powder evenly over the cold water. Do not stir. Let it sit undisturbed for 5 to 10 minutes to bloom and hydrate into a firm puck.
Simmer the base: In a medium saucepan, combine the coconut milk, maple syrup, vanilla, and salt. Sift in the matcha powder to prevent clumps. Whisk vigorously over medium-low heat until the matcha dissolves and the liquid is steaming hot (do not boil).
Dissolve the gelatin: Remove the saucepan from the heat. Add the bloomed gelatin puck and whisk gently for 60 seconds until completely dissolved.
Temper the yogurt: In a separate bowl, whisk the room-temperature Greek yogurt. Slowly pour in ½ cup of the hot matcha liquid into the yogurt, stirring constantly to temper it. Pour this yogurt mixture back into the main saucepan and whisk until silky smooth.
Strain and chill: Pour the entire mixture through a fine-mesh strainer into a pouring jug. Divide the liquid evenly among 4 glass coupes or ramekins. Cover tightly with plastic wrap and refrigerate for at least 4 hours (or overnight) until fully set.
Garnish: Just before serving, uncover and garnish with finely crushed pistachios and a light dusting of extra matcha powder. Serve chilled.