In a large bowl or resealable bag, combine the chicken thighs with olive oil, minced garlic, Meyer lemon zest and juice, dried oregano, dried thyme, cumin, paprika, salt, and black pepper. Massage the marinade into the meat until each piece is well coated. Cover and refrigerate for at least 1 hour, or overnight for more intense flavor.

Meanwhile, prepare the tzatziki: grate the cucumber and squeeze it firmly in a clean kitchen towel to remove as much liquid as possible. In a medium bowl, stir together the Greek yogurt, drained cucumber, minced garlic, fresh dill, lemon juice, olive oil, and a pinch of salt and pepper. Cover and chill until ready to serve.

Heat a grill or a large cast-iron skillet over medium-high heat. Cook the marinated chicken thighs until golden brown and cooked through, about 4 to 5 minutes per side, depending on thickness. Transfer to a cutting board, tent loosely with foil, and let rest for 5 minutes before slicing into thin strips.

Warm the pita breads in a dry skillet, toaster oven, or on the grill for about 1 minute per side, until soft and pliable. Keep them wrapped in a clean towel to stay warm.

Lay a warm pita on a plate and spread a generous spoonful of tzatziki down the center. Add slices of the rested chicken, then top with red onion, tomato, and shredded lettuce.

If desired, sprinkle crumbled feta cheese over the filling, add a few cucumber slices, and finish with fresh parsley. Fold the pita over the filling or serve open-faced.