Place the cashews in a heatproof bowl and pour over boiling water until completely covered. Let them soak for 20 minutes to soften (if you don't have a powerful blender, you'll need to soak them longer). Drain and rinse the cashews before adding them to the base of your blender along with the fresh water and a tiny pinch of salt.
Blend on high until smooth and creamy. Depending on the power of your blender, you may need to scrape down the sides or use the tamper (if your blender has one) to get it completely smooth.
In a medium bowl, mix together the cashew cream, lemon zest, fresh lemon juice, thinly sliced green onions, fresh dill, and freshly cracked black pepper.
Flake the salmon and fold it into the cashew cream mixture, along with the capers. For the best flavor and texture, let sit at room temperature for a few minutes before serving.