Step 1
In a large bowl, combine marinade ingredients and stir well.
Step 2
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.
Step 3
Preheat oven to 400°F (200°C).
Step 4
In a medium bowl, combine tzatziki ingredients and stir well. Cover and refrigerate at least 30 minutes.
Step 5
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. Bake for 1.5 to 2 hours, until internal temperature reaches 165°F (75°C). Let cool for 10 minutes.
Step 6
Carve off slices of chicken to fill a pita. Top with onion slices, tomato slices, and tzatziki sauce.
Step 7
Enjoy!