Peel the cucumber then cut lengthwise. Using a teaspoon, scape off and discard the seeds. Finely grate cucumber.
Place the grated cucumber in a piece of cheesecloth. Gather the edges of the cheesecloth then squeeze out as much water as you can. Place the grated cucumber in a mixing bowl.
Peel the garlic and grate. Add to the cucumber.
Stir in the yogurt to the cucumber and garlic.
Grate the zest of the lemon directly over the yogurt mixture.
Squeeze the lemon juice into the yogurt mixture.
Sprinkle in the dill and stir.
Serve the tzatziki cold.