English cucumbers tend to be sweeter than regular cucumbers; they also have smaller and less seeds than a regular cucumber, which makes it easier for this recipe.
Peel the cucumber then remove the seeds it by cutting the cucumber in half lengthwise. Use the tip of a teaspoon to gently scrape the seeds from the center of each half. Grate the cucumber into a medium mixing bowl.
Drain the grated cucumber in a mesh strainer and pat with a towel until it is completely dry (otherwise the tzatziki will come out watery, especially if you use a lower fat Greek yogurt.)
In a medium bowl slowly whisk the Greek yogurt, grated cucumber, garlic, lemon zest, lemon juice, sugar and dill. Season to taste with salt.
Cover and refrigerate until ready to serve. The tzatziki can be made up to a week in advance.