You can buy drained yogurt at Greek food shops. Substitute fresh dill or parsley for the mint if you like. Raita is the Indian version of this sauce. To make it, just reduce the garlic and dice the cucumber instead of grating.
Add the yogurt to a colander lined with cheesecloth and place over a bowl. Drain for a minimum of 2 hours or overnight in the refrigerator. If you don’t drain the yogurt, the tzatziki sauce will be looser.
Drain the grated cucumber and squeeze out the excess liquid. Mix yogurt with remaining ingredients. Season the mixture with salt and pepper and stir in the chopped mint. Makes about 1 ½ cups.