Place the cashews, water, lemon juice and garlic into a blender and blend* on high until smooth. Puree should be as smooth and thick as Greek yogurt. If you cant get it smooth you can strain out any larger pieces, or leave them in for a chunkier Tzatziki.
Peel the cucumber then grate it using a cheese grater.
Put the cucumber into a colander, sprinkle with salt and let it drain into a bowl/sink for 20 minutes.
Squeeze out the excess water and mix the cucumber, dill and chives into the cashew puree.
Serve right away* or chill. Preparation time will vary depending on this step.