Combine tahini, oil, lemon juice, shallot, garlic, agave nectar, yogurt, vinegar, and 1/4 cup water in a blender and puree until smooth, adding more water if needed to make dressing pourable. Add cayenne and season to taste with salt and pepper(if using).
To make salad:.
Place the cucumber in a small bowl, top with enough of dressing to coat generously, and then sprinkle with the mint and parsley. Toss to combine. Serve and enjoy!