1. Shred cucumber. Don't worry about getting all of it shredded; if there is nub left, cut it up and toss it in with the sour cream at the end.
2. Put the sour cream into whatever you're going to keep/make the tzatziki in. (I use Tupperware) The cucumber shreds should be sitting in a bunch of liquid from the cucumber.
3. Taking small handfuls at a time, squeeze the liquid out of the cucumber and then put the shreds into the sour cream. Don't worry about squeezing every last drop out, or the Tzatziki might be too thick.
4. Now add the rest of the ingredients and stir well. Let sit in the fridge for at least an hour to let the flavors mingle. (I'm not sure how necessary this is, but I think it's better that way).
Source of recipe: I made this recipe to go with seitan gyros and falafel. Tzatziki's usually made with yogurt, but it's impossible to get plain soy yogurt around here; so I figured I'd make a Tzatziki recipe with sour cream, like most of the Mediterranean restaurants here.