Begin by soaking the cashews in boiling hot water for 30 minutes. This helps to soften the cashews so they are easier to blend and creamier. NOTE- you will need a high-speed blender for the tzatziki.
Once the cashews have soaked for 30 minutes, grate 1/2 of a cucumber over a towel or paper towel (you can leave the skin on it will just give the Tzatziki a bit of a green hue). Once grated, bundle the cucumber up in the towel it's on, and squeeze out as much of the water as you can. Set aside.
Drain the water from the cashews and then add the cashews to a high-speed blender along with the lemon juice, water (start with 2 tbsp), garlic, cucumber and salt and pepper. Depending how the blending process goes, and how thick you want your Tzatziki, add 1 more tbsp of water. Blend until smooth.
Lastly, fold in the dill. Best eaten fresh. But can store in the fridge for a few days.