TZATZIKI SAUCE: Using the large holes of a box grater, shred cucumber; dab with paper towels and set aside.
In a medium non-reactive bowl, whisk together all ingredients except the cucumber. Stir in the cucumber and refrigerate until ready to serve.
GREEK LEMON CHICKEN: In a large non-reactive bowl, whisk together lemon juice, red wine vinegar, olive oil, garlic, oregano, parsley, coriander, salt and pepper. Add cubed chicken; toss to coat. Cover and refrigerate the chicken for 1 to 2 hours.
Thread the chicken onto metal or wooden skewers. Note: If using wooden skewers soak in cold water for 30 minutes.
Preheat the grill to medium high heat. Oil the grates of the grill or grill pan and place the skewers on them.
Grill the chicken for 3-4 minutes, flip kebabs over and grill for another 3-4 minutes or until the chicken is cooked through.
Serve kebabs with pita or naan bread and Tzatziki sauce.