GotGarlic et al have pretty much nailed it - if you wanted to do a web search look for tzatzki and yes, it's like spaghetti sauce in that there are as many recipes as there are cooks. I used Alton Brown's recipe when I made gyros last year per his oven method- go to Food Network : Healthy Recipe Collections, Party Ideas, Quick & Easy Recipes, Cooking Videos and search gyros. There are several good sauce recomendations.