You should start making the dip maybe five or six hours ahead of when you plan to serve it. I found the leftovers kept well refrigerated for 24 hours, so you could probably prepare it that far in advance. It will just need a good stir before serving.
The first step is to find a good, thick plain yogurt (500 mL). I prefer at least 2% milk fat in mine, more if I can find it. (What makes non-fat yogurt so creamy? It freaks me out.) Greek-style is preferable as it is the thickest type of yogurt, but I could only find Balkan-style and it still worked well. So, as I mentioned, you need to get rid of any excess moisture in the yogurt. This can be accomplished using a large bowl and a strainer lined with cheesecloth. This is my set up:
I used the large side of a plain old box grater and grated one English cucumber, skin and all (for the colour and the nutrients). To get rid of the excess water, just use a bit of basic science: sprinkle the grated cuke with salt (a teaspoon or two), which will osmotically draw water out of its cells. Give the process time to work by leaving the mixture in the fridge for an hour or so. Next, to get rid of the moisture, drain the liquid out of the mixture, then pat it down well with some paper towels or a clean dish towel. The cucumber shreds should look pretty limp and relatively dry.
[just-salted cuke]
From here on out, the recipe is pretty basic. Mix the thickened yogurt with the dry cucumber, then add a clove (or more to taste) of crushed garlic and the juice of 1/2 lemon, plus some zest. Stir well. Chill for a few hours before serving.
[clockwise from top: whole-wheat pita bread, tzatziki, tabouleh, hummous, kibbeh]
Hope you find an opportunity to prepare this great dip!