For the chicken:
For the tzatziki:
- Place the chicken and all marinade ingredients in a large bowl. Toss to combine and coat the chicken pieces evenly. Let sit in fridge for at least 30 minutes, up to 2 hours.
- Meanwhile, make the tzatziki: Place the grated watermelon rind in a bowl lined with a paper towel. Squeeze as much liquid as you can out of the rind, then discard the liquid. Place the rind in a bowl with the remaining tzatziki ingredients and stir to combine.
- Heat the broiler to high and remove chicken from the fridge. Spread the chicken on a greased baking sheet and pat with paper towels to remove much of the liquid from the marinade. Broil for 8-10 minutes, until the chicken is browned and cooked through.
- Assemble gyros by filling the pita or flatbread with lettuce, tomatoes, red onion, parsley, and chicken, then spooning the tzatziki over the top. Enjoy!