Chop chicken into bite sized pieces. In a medium mixing bowl, combine all marinade ingredients and stir to combine thoroughly. Add chicken and mix to coat. Let marinate 30 minutes up to 6 hours.
To make Tzatziki, add all ingredients into a small mixing bowl and taste, adjusting seasonings as desired.
To assemble each sandwich, layer some lettuce onto the pita, then add chicken, spoon some tzatziki, and then add your sliced cucumber, tomato, and onion. Finish with some crumbled feta and fresh dill (and you can add a squeeze of lemon if desired). Enjoy!