01 - In a mixing bowl, whisk together the olive oil, lemon juice, minced garlic, cumin, smoked paprika, coriander, oregano, cayenne pepper (if using), salt, and black pepper. Add the sliced chicken and toss thoroughly to coat. 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, fresh dill, grated garlic, and season with salt and pepper to taste. Stir until smooth and well blended. Cover and refrigerate until ready to serve.
03 - Heat a grill pan or large skillet over medium-high heat. Add the marinated chicken in an even layer and cook for 6 to 8 minutes, stirring occasionally, until the chicken is cooked through and lightly charred on the edges. Remove from heat and set aside.
04 - Warm each pita bread briefly in a dry skillet over medium heat for about 30 seconds per side, or microwave 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 pitas immediately while warm. Offer extra lemon wedges on the side for squeezing over the filling.