A stable of gyros, cucumber sauce is something I find myself almost always keeping in my fridge. It goes wonderfully with pita bread, chicken, beef, and lamb.
More often than not, I make this recipe by taste. I strongly suggest that you do too! Just remember that the flavors get stronger when they're allowed to sit in the fridge, so make the sauce ahead of time for optimal taste.
You can use greek yogurt, yogurt, or sour cream as the base for your sauce. If you use ordinary yogurt, then you will want to drain it for optimal consistency. If you're using greek yogurt or sour cream, skip ahead to prepping your cucumber.
To drain your yogurt, let it sit in a colander over the sink or a bowl to collect the liquid. If the collander's holes are too big, cover them with a paper towel.
Peal and de-seed your cucumber. If you like chunks of cucumber in your sauce, you can then just chop it finely by hand. If you are like me and don't actually much like cucumber, then you might want to chop it up in a food processor.
Add the cucumber to the yogurt, and then season it with dill, garlic, salt, and pepper to taste.
Make it ahead of time to let the flavors mix in the fridge before serving!