In a large bowl, combine marinade ingredients and stir well.
2. Step
On a cutting board, place a piece of plastic wrap over the chicken thighs and pound until about ½ inch (1 cm) thick with a meat mallet, rolling pin, or heavy pan.
3. Step
In another large bowl or gallon plastic bag, combine chicken thighs and marinade, stirring well to coat. Cover and refrigerate for at least one hour and up to one day.
4. Step
Preheat oven to 400°F (200°C).
5. Step
Shred the cucumber, be sure to squeeze out any excess liquid.
6. Step
In a medium bowl, combine tzatziki ingredients and stir well. Cover and refrigerate at least 30 minutes.
7. Step
On a baking sheet or a large cast-iron skillet, use the onion half as a base and position the skewer vertically like a spit. Skewer the chicken thighs individually, rotating each one 90 degrees.
8. Step
Bake for 1.5 to 2 hours, until internal temperature reaches 165°F (75°C). Let cool for 10 minutes.
9. Step
Carve off slices of chicken to fill a pita. Top with onion slices, tomato slices, and tzatziki sauce.
