To make the tzatziki sauce, strain the yogurt using cheesecloth over a bowl. Let strain for several hours or overnight, if possible, to remove as much moisture as possible. (You won't believe how much liquid drains from the yogurt - it makes the yogurt much thicker and creamier. If you want to splurge on Greek yogurt, like Oikos, you won't need to strain it like this.)

Shred the cucumber. Wrap in a towel a squeeze to remove as much water as possible. Mix together the strained yogurt, shredded cucumber, garlic, red wine vinegar, salt and pepper to taste, and lemon juice. Drizzle lightly with olive oil. Refrigerate for at least 30 minutes before serving to allow the flavors to meld.

To prepare the chicken, combine the garlic, lemon juice, red wine vinegar, olive oil, yogurt, oregano, and salt and pepper to taste in a medium bowl. Whisk together until mixed well. Add the chicken pieces to the bowl and mix well to coat. Cover and refrigerate for about 1 hour.

Cook the chicken as desired, either in the skillet or with the broiler. (Melanie sauteed them in a hot skillet, I cooked mine on the grill) Once the chicken is completely cooked through, transfer to a plate and let rest for 5 minutes.

Heat pitas. Top with chicken, tzatziki sauce, diced tomatoes and sliced onions. Serve immediately.