marination period. About 30 minutes before serving, drain off and discard the marinade. Thread the chunks of meat onto long skewers, brushing with a little olive oil. (We usually BBQ the peppers and tomatoes on separate skewers but it's really up to the chef.) Over medium coals, barbeque the souvlaki until it's done the way you like it. Serve on a bed of rice and pass the tzaziki to spoon on top. SERVES 4-6 TZAZIKI: Line a colander or sieve with cheesecloth (or gauze) and set it over a bowl. Pour in the yogurt and allow it to drip for an hour or so. After the yogurt has drained, combine it, in a small bowl, with the cucumber and the garlic. Cover the bowl tightly with plastic wrap and refrigerate until just before serving. While the meat is BBQing, drizzle the olive oil over the surface, and without stirring, sprinkle on the salt. It needs no mixing your guest will do that when they dollop it onto their souvlaki. MAKES: About 3 cups