prep the chicken: pound the chicken down to an even thickness using a mallet or rolling pin, cover the chicken with plastic wrap first.
to make the marinade combine balsamic, olive oil, oregano, garlic and onion powder and place into a plastic bag or dish large enough to cover the chicken. Add the chicken and season with salt and pepper. Add more olive oil if needed to ensure the chicken is fully covered. Refrigerate 1 hour.
Preheat the grill to 350 degrees F.
To make the salsa topping: combine diced cucumber, olives, tomatoes, red onion and dill in a bowl. Season with a touch of salt and pepper and the lemon juice. Set aside until ready to assemble.
To cook the chicken, grease the grill with some cooking spray or brush with oil. Place chicken breast side down directly on the grill. Let side for 3-4 minutes and flip. Cook the other side for 3-4 minutes or until internal temperature reaches 165 degrees F. Remove from the grill and let rest for 10 minutes. Once rested slice the chicken into thin strips.
Leave the grill on and toss those pitas directly on the grill to warm right before assembling. Heat for 30 seconds to 1 minute until just warmed.
To serve: spread some tzatziki across the bottom of each pita, layer with shredded lettuce, top with chicken strips and finish with the salsa and extra tzatziki. Enjoy!