01 - In a mixing bowl, whisk together the olive oil, lemon juice, minced garlic, cumin, smoked paprika, coriander, oregano, cayenne (if using), salt, and black pepper. Add the sliced chicken and toss until evenly coated. Cover and refrigerate for at least 15 minutes, or up to 8 hours for deeper flavor penetration.
02 - In a small bowl, combine the Greek yogurt, lemon juice, chopped dill, grated garlic, and season with salt and pepper to taste. Stir until smooth, cover, and refrigerate until ready to serve.
03 - Heat a grill pan or large skillet over medium-high heat. Remove the chicken from the marinade, allowing excess to drip off, and cook for 6 to 8 minutes, stirring occasionally, until the chicken is cooked through and lightly charred on the edges. Transfer to a plate and rest briefly.
04 - Warm each pita bread in a dry skillet over medium heat for about 30 seconds per side, or microwave individually for 15 seconds until pliable.
05 - Open each warm pita and layer with shredded romaine lettuce, diced cucumber, halved cherry tomatoes, and sliced red onion. Spoon the cooked chicken on top and drizzle generously with the prepared yogurt sauce.
06 - Serve the stuffed pitas immediately, accompanied by extra lemon wedges on the side if desired.