In a medium bowl, whisk the lemon juice, olive oil, oregano, thyme, garlic, salt, and pepper. Add the chicken, toss to coat, cover, and refrigerate for 30 minutes.
Remove the chicken from the bowl and discard the marinade.
Spray a large nonstick skillet well with cooking spray, add the chicken and cook until the pieces are completely cooked through, about 8 minutes. Transfer to a plate.
In a small bowl, combine the yogurt and dill.
Lay the pita bread on a work surface and spread half of the tzatziki on each. Divide the chicken among the pitas, followed by the romaine, cucumber, tomato, feta, a bit of fresh parsley. Fold and serve!