Preheat the oven to 425°F. Line a sheet pan with aluminum foil.
Toss the chicken on the sheet pan with ¼ cup of the olive oil, the lemon juice, garlic powder, smoked paprika, coriander, cumin, turmeric, cinnamon, cayenne (if using), 2 teaspoons salt, and 1 teaspoon pepper until well coated. (Alternatively, you can marinate the chicken in the refridge for up to 8 hours, then bring to room temperature before cooking.)
Add the remaining 2 tablespoons oil to the sheet pan along with the cauliflower, onion, and ½ teaspoon salt and toss with the chicken to coat well. Spread into an even layer and roast until the chicken and cauliflower are golden brown and cooked through, 30 to 40 minutes. (If you'd like more browning, broil for a few minutes.)
If serving with pita, wrap the pita in aluminum foil; when the chicken's done, set it aside briefly and transfer the pita to the oven to warm for about 5 minutes. Thinly slice the chicken and eat with the cauliflower, onion, and any accompaniments you like.
