Add chicken to a large bowl or ziplock bag. Combine marinade ingredients and pour over chicken. Stir well to coat and marinate for 1-4 hours.
Meanwhile, make the tzatziki sauce by combining all ingredients. Taste it and add more seasoning (lemon juice, garlic, salt, pepper or cumin)if needed. Refrigerate.
Heat grill to medium and oil the grates (or if cooking on the stove, add a little oil). Remove chicken from marinade, letting any excess sauce drip off.
Grill chicken for a few minutes on each side, flipping once, until cooked through. Remove to a plate to rest before chopping into bite-size pieces.
Toast or warm your pitas. Layer with chicken, lettuce, tomato, red onion, cucumber and sauce. Enjoy!
