Sprinkle the grated cucumber with salt and set aside for 10 minutes to rest (you can begin the remaining steps while you wait). After the cucumber has rested, place it in a clean dish towel and squeeze out the excess moisture over a sink. You want it to be fairly dry.
To soften the cashews, boil water in a small pot and remove from heat. Add cashews and cover for 15-20 minutes. Drain and rinse the cashews and discard soaking water. Alternatively, you can let the cashews soak in cool water in the fridge for 3-4 hours or overnight. (*If your blender is very powerful, you don't have to soak the cashews).
Add the yogurt, lemon juice, cashews, garlic, olive oil, vinegar, salt, and pepper to a high-powered blender. Blend on high until creamy and smooth, scraping down sides as needed. Taste and add more lemon or vinegar if needed. Wait to add more salt though.
Pour the mixture into a small bowl and stir in the cucumber, dill, and mint. Combine well. Taste and add more seasoning if needed. Cover and place in the fridge for at least 30 minutes to develop more flavor.
After chilling, give it a good stir. The consistency should be thick, but if you want to thin it out a little, add a splash of water and stir well. To serve, top with a few kalamata olives, fresh-cut mint, or dill, and a swirl of olive oil if desired.