Finely grate the cucumber on the small holes of a grater. Use 1/2 cup of grated cucumber an place it in a paper towel to squeeze out excess moisture.
In a medium mixing bowl, combine all of the ingredients and stir well to combine. Chill until ready to serve.
Notes
Storage: Store leftover tzatziki sauce in an airtight container in the refrigerator for up to 4 days. Stir to redistribute the ingredients before serving, and add a small squeeze of fresh lemon if needed to brighten it back up.