Mix all ingredients in a medium bowl and whisk to combine
Add 4 Boneless Skinless Chicken breasts to marinade and stir to coat. Cover and refrigerate for 30 min-24 hours.
To cook the chicken:
Preheat grill to 400 degrees. Spray grill with nonstick cooking spray so chicken doesn’t stick to grates.
Remove chicken from marinade and grill for 5-7 minutes a side or until chicken is cooked to 165 degrees.
Remove chicken breasts from grill and cover with foil for 10 minutes to let juices redistribute.
Slice chicken into strips and serve with gyros toppings.
To assemble the gyros:
On top of flatbread, spread desired amount of tzatziki sauce and top with grilled chicken slices. Add desired amount of diced tomatoes, red onion and chopped cucumber on top. Roll and serve immediately.