In a large bowl, whisk together yogurt, minced garlic, ground cumin, ground coriander, smoked paprika, cinnamon, lemon juice, olive oil, salt, and pepper until smooth. Add boneless chicken thighs, ensuring each piece is well coated. Cover and refrigerate for at least 1 hour or overnight.

Preheat the grill or oven to 425°F (220°C). If using the grill, ensure it's clean and oiled. If baking, line a baking sheet with parchment paper.

Remove chicken from fridge and place it on the grill or baking sheet. Grill each side for 5–7 minutes until golden brown and internal temperature reaches 165°F (75°C), or roast for 20-25 minutes if baking.

Once cooked, remove the chicken and let it rest for 5–10 minutes. Slice the chicken into thin strips against the grain.

To assemble, take a warm pita bread and layer with fresh vegetables, sliced chicken, a drizzle of tzatziki, and pickled onions. Wrap tightly and serve immediately.